Columbia  ®mbergitp^  ^ 

^cljool  of  Bental  anb  (j^ral  burger? 


i^eference  l^ibrarp 


DENTAL  AND  ORAL  RADIOGRAPHY 


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in  2010  witii  funding  from 

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DENTAL  AND  ORAL 

EADIOGRAPHY 


A  TEXTBOOK  FOR  STUDENTS  AND  PRACTITIONERS 
OF  DENTISTRY 


BY 


JAMES  DAVID  McCOY,  D.D.S. 

PROFESSOR    OF   ORTHODONTIA    AND    RADIOGRAPHY,    COLLEGE    OF    DENTISTRY, 
UNIVERSITY   OP    SOUTHERN    CALIFORNIA,    LOS    ANGELES,    CALIFORNIA 


WITH  123  ILLUSTRATIONS 


SECOND  EDITION 


ST.  LOUIS 

C.  V.  MOSBY  COMPANY 

1919 


n 


Copyright,  1916,   1918,  bv  C.  V.  Mosby   Company 


Press  of 

C.    V.   Mosby   Comf^any 

St.    Louis,    Mo. 


PREFACE  TO  SECOND  EDITION 

During  the  preparation  of  the  second  edition  of  this  book  the 
author  has  endeavored  at  all  times  to  keep  in  mind  the  needs  of 
the  beginner  in  radiography  rather  than  consider  matters  of  in- 
terest to  those  who  have  progressed  beyond  this  stage. 

That  radiography  is  essential  in  the  practice  of  dentistry  is 
no  longer  a  debatable  question.  The  wide  interest  being  mani- 
fested in  it  by  our  profession  and  the  numerous  instances  where 
dentists  are  installing  their  own  x-ray  laboratories  bear  elo- 
quent testimony  of  this  fact.  While  the  author  is  willing  to  plead 
"guilty  to  a  great  degree  of  enthu.siasm"  regarding  the  value 
of  the  x-ray  in  dentistry,  he  feels  that  he  is  within  reasonable 
bounds  in  asserting  that  the  x-ray  has  done  more  to  improve 
dentistry  than  any  other  agent  that  has  come  into  it  during  the 
past  ten  years.  If  it  were  of  value  ''in  root  canal  operations 
only"  the  benefits  to  this  field  alone  would  justify  the  foregoing 
statement,  for  we  must  all  acknowledge  that  as  commonly  prac- 
ticed in  the  past  this  branch  represented  the  greatest  short- 
coming of  our  profession. 

Fortunately  root  canal  work  does  not  represent  the  only  field 
in  dentistry  where  the  radiogram  is  a  benefit,  for  it  has  been 
demonstrated  that  it  is  of  equal  value  and  in  fact  is  often  abso- 
lutely essential  in  the  other  branches  of  practice.  These  facts 
are  not  only  now  fairly  well  appreciated  by  dentists,  but  the 
laity  have  been  quick  to  grasp  them  with  the  result  that  den- 
tists who  attempt  certain  operations  witiiout  radiographic  guid- 
ance are  open  to  censure  from  their  patients. 

The  awakening  of  the  rank  and  file  of  the  profession  to  the 
necessity  of  a  more  universal  adoption  of  the  x-ray  has  been 
slow,  and  it  is  doubtful  if  some  will  ever  become  fully  conscious, 
as  they  continue  to  exhibit  a  lethargy  toward  this  field  which 
is  either  indicative  of  lack  of  foresight  or  sheer  laziness. 

In  contrast  to  such,  it  is  refreshing  to  recall  that  some  mem- 
bers of  our  profession  were  quick  to  see  the  possibilities  to  den- 

5 


6  PREFACE 

tistry  offered  through  the  adoption  of  the  x-ray.  Conspicuous 
among  these  was  Dr.  C.  Edmond  Kells,  of  New  Orleans,  who  in 
1896  (within  the  year  following  the  discovery  of  the  x-ray) 
installed  x-ray  equipment  in  his  office  and  applied  it  to  his 
dental  practice.  So  great  were  his  convictions  and  so  genuine 
was  his  enthusiasm  that  in  July,  1906,  he  took  his  x-ray  equip- 
ment to  Ashville,  N.  C,  and  there  gave  a  clinic  before  the  South- 
ern Dental  Association.  Dr.  Kells  w#s  the  first  dentist  to  make 
radiograms  by  placing  small  films  in  the  mouth,  and  he  also 
originated  the  plan  of  placing  diagnostic  wires  in  the  roots  of 
teeth. 

Among  those  who  shared  Dr.  Kells'  foresight  during  those 
pioneer  days  and  adopted  the  x-ray  as  part  of  dental  practice 
are  numbered  such  men  as  Drs.  Van  Wort,  M.  L.  Rhein,  E.  W. 
Caldwell,  T.  P.  Hinman,  and  "Weston  A.  Price. 

Within  the  last  few  years  a  large  number  of  our  dental  schools 
have  included  radiography  in  their  teaching  eurriculums  and 
some  have  even  shown  the  foresight  of  establishing  it  as  a  dis- 
tinct department  with  equal  rank  and  consideration  with  the 
other  important  branches.  This  will  in  time  bear  fruit  which 
will  result  in  a  more  adequate  appreciation  of  the  merits  and 
possibilities  of  the  x-ray  and  its  inseparable  relationship  to 
dentistry. 

The  author  wishes  to  gratefully  acknowledge  the  assistance 
given  him  in  the  preparation  of  this  edition  by  Dr.  Julio  Endel- 
man,  whose  friendly  criticism  and  interest  have  been  a  constant 
source  of  help.  Grateful  acknowledgment  is  also  made  to  Dr. 
Richmond  C.  Lane,  who  was  kind  enough  to  contribute  several 
radiograms  from  practical  cases  illustrating  root  canal  opera- 
tions, root  resections,  and  cysts.  The  author  has  also  been  aided 
by  various  manufacturers  of  x-ray  equipment  who  have  fur- 
nished many  cuts  of  value  to  the  text,  and  last,  but  not  least, 
the  publishers  have  by  their  cooperation  and  patience  through 
many  delays  rendered  less  irksome  the  task  of  the  w^riter. 

James  D.  McCoy. 

Los  Angeles,  Cal. 


PREFACE  TO  FIRST  EDITION 

This  book  has  been  written  primarily  as  a  textbook  for  stu- 
dents of  dentistry.  It  is  essentially  a  book  for  beginners,  and 
as  the  majority  of  the  dental  profession  are  at  present  to  be 
regarded  as  beginners  in  this  comparatively  new  branch  of  den- 
tistry, the  author  entertains  the  hope  that  it  will  prove  of  inter- 
est to  practicing  dentists  who  appreciate  the  value  of  the  x-ray, 
and  are  desirous  of  adding  radiography  to  their  accomplish- 
ments. 

A  few  years  ago  the  x-ray  was  considered  in  the  light  of  a 
cultural  asset  to  dentistry,  but  today  the  far-seeing  members 
of  our  profession  have  awakened  to  the  fact  that  it  is  a  real 
necessity. 

The  x-ray  will  give  the  maximum  amount  of  service  in  dental 
practice  only  to  such  of  our  profession  who  master  the  technic 
of  radiography,  and  in  addition  are  possessed  of  an  accurate 
knowledge  of  the  anatomy  and  pathology  of  the  dental  and  oral 
structures. 

The  author  is  indebted  to  the  pioneers  in  dental  radiography 
who  have  so  generously  contributed  to  its  literature.  Of  these, 
much  of  value  has  been  derived  from  the  writings  of  such  men  as 
Drs.  A.  H.  Ketcham,  Weston  Price,  Sidney  Lange,  Howard  R. 
Paper,  F.  L.  P.  Satterlee  and  Edward  H.  Skinner. 

During  the  preparation  of  this  work,  the  author  has  been 
aided  by  various  manufacturers  of  x-ray  equipment  who  have 
generously  furnished  cuts  whenever  requested.  G-rateful  ac- 
knowledgment is  also  made  to  Dr.  J.  P.  McCoy  and  to  Laura 
Spruill  who  have  made  the  drawings  used  as  illustrations,  and 
last  and  by  no  means  least,  to  the  publishers  who  have,  through 
their  forbearance  and  many  courtesies,  lessened  the  burdens  of 
the  writer. 

James  D.  McCoy. 

Los  Angeles,  Cal. 


CONTENTS 

PAGE 
CHAPTER  I 

Introduction 17 

CHAPTER  II 

The  Nature  of  the  X-ray  and  Its  Discovery 22 

CHAPTER  III 

High  Tension  Electric  Currents — Magnetism — Electromagnetic 

Induction 31 

CHxVPTER  IV 

RlIUMKORFF   OR   INDUCTION   COIL — TESLA  OR   HiGII    FREQUENCY   COIL — 

Interrupterless  Transformer 43 

CHAPTER  V 

Requisites  op  the  Dental  X-ray  Laboratory 62 

CHAPTER  VI 

Teciinic   of  Dental  and   Oral   Radiography 88 

CHAPTER  VII 

Teciinic  of  Dental  ant)   Oral  Radiography    (Continued)     .     .     .     107 

CHAPTER  VIII 

Correct  Exposure  and  Development  of  X-ray  Plates  and  Films     115 

CHAPTER  IX 
The  Interpretation  op  Dental  and  Oral  Radiograi.es     ....     122 

CHAPTER  X 

Indications    for.  the   Use    of    the    X-ray   in    the    Practice    op 

Dentistry 135 

CHAPTER  XI 

Dangers  of  the  X-ray  and  Methods  of  Protection 167 

9 


ILLUSTRATIONS 

FIG.  PAGE 

1.  William    Conrad   Roentgen 24 

2.  Michael   Faraday 25 

3.  Sir   William   Crookos 26 

4.  Ilcinrich    Hertz 27 

5.  The  action  of  iron  filings  in  forming  definite  curved  lines  about 

an    ordinary    bar    magnet 35 

6.  Diagrammatic  illustration  of  the  magnetic  lines  of  force     .     .     .  3G 

7.  Diagrammatic   illustration    of   the   magnetic   field   surrounding    a 

coil  of  wire  through  which  an  electric  current  is  passing     .     .  37 

8.  An  iron  bar  placed  within  the  windings  of  a  solenoid  is  subject 

to  its  magnetic  field  and  becomes  a  magnet 38 

9.  Magnet   with    diagrammatic   illustration    of    ''magnetic    lines    of 

force"   surrounding   it 39 

10.  Battery   from   which  an   electric   current  is   passing   through   the 

solenoid        40 

11.  Diagrammatic  illustration  of  the  essential  parts  of  an  induction 

coil 44 

12.  Diagram    of    the   electrolytic   interrupter 46 

13.  Diagram    of    the    induction    coil 47 

14.  Induction  coil  adapted  for  use  in  the  dental  x-ray  laboratory     .     .  49 

15.  Induction  coil  adapted  for  use  in  the  dental  x-ray  laboratory     .  50 

16.  Induction  coil  adapted  for  use  in  the  dental  x-ray  laboratory     .  51 
3  7.     Diagram   of   the   high   frequency    coil 54 

18.  Small   type   high   frequency   coil 55 

19.  Medium-sized  high  frequency  coil 55 

20.  Large   type  high  frequency   coil 56 

21.  The  working  principles  of  the  interrupterless  transformer     ...  57 

22.  Interrupterless  traiif-former  adapted  for  use  in  the   dental  x-ray 

laboratory 58 

23.  Interrupterless  transformer  adapted  for  use  in  the  dental  x-ray 

laboratory 59 

24.  Interrupterless  transformer   adapted  for  use  in  the  dental  x-ray 

laboratory 60 

25.  Diagram  of  an  x-ray  tulje 65 

26.  The  coil  or  transformer  tube 66 

27.  The  high  frequency  tube 67 

28.  Connecting   tube   to   x-ray   machine 68 

29.  The  hydrogen  tube 68 

30.  The  Coolidge  x-ray  tube 69 

31.  The   tube   stand 71 

11 


12  ILLUSTRATIONS 

FIG.  PAGE 

32.  Illustrating  liow  the  tube  may  be  placed  at  any  desired  angle     .  72 

33.  Illustrating  reasons  for  using  the  tube  shield,  compression  dia- 

phragm, and  compression  cylinder 78 

34.  Leadipd   glass    tube    shield 74 

35.  A  convenient  manner  of  arranging  the  necessary  ajiparatus  when 

not  in  use 75 

36.  The  portable   darkroom 77 

37.  The  patient  holding  the  film  in  position  against  the  upj)er  teeth  82 

38.  Correct  and  incorrect  technic 83 

39.  Technic  for  the  upper  molar  teeth 85 

40.  Special  compression  cylinder  made  of  leaded  glass 86 

41.  The  patient  holding  the  film  in  position  against  the  lower  teeth  87 

42.  The   Ketcham  film  holder 89 

43.  The  Leach  film   holder 90 

44.  The  Dorr  film  holder  with  detachable  handle 91 

45.  Procedure  for  making  complete  radiographic  examination  of  den- 

tal   arches 91 

46.  Arrangement   of    dental    chair    allowing   patient's   head    to    rest 

easily  and  firmly  upon  it 93 

47-^.     Tube  stand  with  platerest  and  head  support 94 

47-i?.     Position  of  head  and  angle  for  left  side  of  jaws 94 

48.  The   arrangement   of  the   apparatus   prei^aratory  to    seating   the 

patient        95 

49.  The  patient  seated   and   the   apparatus   arranged   for   making   a 

radiogram   of  the  left   side 95 

50.  Technic  for  left  side 98 

51.  Technic  for   right   side 99 

52.  The  result  of  correct  technic 100 

53.  Incorrect    technic 101 

54.  The  result  of  incorrect  technic 102 

55.  Technic   for  radiographing   areas  in   the   upper   and  lower   jaws 

extending  from  the  median  line  to  the  first  premolar     .     .     .  103 

56.  Technic  for  radiographing  structures  at  the  median  line  includ- 

ing the  incisors,  both  above  and  below 104 

57.  Supporting  the  patient's  head  by  a  bandage  of  gauze  to  insure 

perfect   immobility 105 

58.  Connecting  the  tube  to  the  x-ray  machine 109 

59.  Diagram    of    an    x-ray    tube 112 

60.  X-rayproof  film  and  plate  chest 116 

61.  Eadiographic    appearance    of    the    teeth    and    their    surrounding 

structures   under  normal   conditions 124 

62.  A  cuspid  tooth  lying  against  the  anterior  wall  of  the  antrum     .  127 

63.  A   radiogram   to   determine  the   state   of   dentition   of   the  right 

side  in  the  mouth  of  a  child  eleven  years  old- 127 


ILLUSTRATIONS  16 

FIG.  PAGE 

64.  An  alveolar  abscess  involving  the  roots  of  an  upper  central  in- 

cisor  and   latei'al   incisor 128 

65.  Eadiogram  showing  evidence  of  an  alveolar  abscess 128 

66.  Large  alveolar  abscess  about  the  root  of  a  lower  first  bicijspid  128 

67.  An  upper  bicuspid  tooth  with  an  alveolar  abscess  at  its  root  apex  129 

68.  Small  abscesses  at  the  apices  of  two  upper  bicuspid  teeth     ,     .  130 

69.  A  necrotic  area  about  the  roots  of  an  upper  central  and  lateral  1.30 

70.  A  necrotic   area  lying    below   a  lower   cuspid 131 

71.  Eoot  canal  fillings  in  a  lower  first  molar 132 

72.  Eoot  canal  filling  material   forced  beyond   the   root   apex  of   an 

upper   second  bicuspid 132 

73.  A  steel  wire  introduced  into  the  root  canal  to  determine  its  length     132 

74.  A   destructive   process   involving   the   pericemental   and   alveolar 

tissues  about  an  upper  first  bicuspid 132 

75.  Characteristic    aj^pearance   of   the   enveloping   tissues    about    the 

upper    bicuspids    and    molars    in    a    well-developed    case    of 

pyorrhea    alveolaris 132 

76.  An  osteosarcoma  of  the  mandible 133 

77.  Well-developed  cyst  over   an  upper  lateral  incisor 133 

78.  Well-developed    cyst   lying    below   the    lower   incisors     ....  133 

79.  Extra-oral   radiogram   of   the   right   side   made   for   purposes   of 

general    examination        137 

SO.     Intra-oral   radiogram   used   as   a   means   of   confirmation   of   the 

findings  of  the  extra-oral  radiogram 138 

81.  Alveolar  abscesses  at  the  apex  of  each  bicuspid  root     ....  138 

82.  Upper  bicuspid  teeth  with   abscesses 138 

83.  Severe    inflammatory    process    in    progress    about    upper    lateral 

incisor        138 

84.  Extra-oral  radiogram  of  the  lower  molars  showing  the  j^i'esence 

of  a  large  alveolar  abscess 139 

85.  Eadiograms   showing  imperfectly   filled   canals,   diagnostic   wires 

in  place,   and  same  teeth  after  being  filled 140 

86.  Eadiograms   showing   imperfectly   filled   canals,   diagnostic   wires 

in  place,  and  same  teeth  after  being  filled 141 

87.  Eadiograms   showing  imperfectly   filled   canals,   diagnostic   wires 

in  place,   and  same  teeth  after  being  filled 141 

88.  Eadiograms  showing  condition  present,  diagnostic  wires  inserted, 

root  canals  filled,  and  resection  of  roots 142 

89.  Eadiograms   showing   central   incisor   before   resection,   after   re- 

section,  and   several  months   later,   showing   regeneration   of 
osseous   tissue 143 

90.  Upper  central  root  before  resection,  and  after  resection,  showing 

partial  regeneration 144 

91.  A  well-developed  case  of   pyorrhea  alveolaris  involving  the  mo- 

lars and  incisors 145 


14  ILLUSTRATIONS 

FIG.  PAGE 

92.  Au   unerupted   cuspid   tooth   making   an   attempt   to   erupt   un- 

der  a  bridge 147 

93.  Eadiogram  made  to  be  sure  no  root  fragments  were  present  in 

the   tissues  under  the  bridge 147 

94.  Inflammatory  process  under   a   small  bridge 147 

95.  Extra-oral  radiograms  of  impacted  and  unerupted  third  molars  149 

96.  Intra-oral  radiograms  of  impacted  lower  third  molars  .  .  .  150 
97-^.  Large  cyst  in  the  mandible  lying  below  a  molar  tooth  .  .  151 
97--B.     Same  case  as  shown  in  Fig.  97-^,  six  months  after  curette- 

ment,  showing  partial  regeneration  of  the  osseous  structure     151 

98.  Large  abscess  with  cyst  formation,  involving  the  upper,  central, 

lateral,    and    cuspid    roots 152 

99.  Eadiogram  revealing  the  fact  that  there  is  a  congenital  absence 

of  permanent  molars  on  the  left  side 153 

100.  Radiogram  revealing  the  fact  that  all  but  one  of  the  permanent 

molars  are  congenitally  absent  on  the  right  side     ....     153 

101.  Unerupted  lower  second  bicuspid  for  which  space  must  be  made 

to    permit    its    eruption 155 

102.  Unerupted  cuspid   for  which   space  must  be   made   if   it   is  to 

erupt  in   its   normal   position 155 

103.  Unerupted  lower  lateral  incisor  for  which  space  must  be  made     156 

104.  Unerupted  lower  second  molar  prevented  from  erupting  through 

impaction  against  the  lower  first  molar 156 

105.  Unerupted  upper   bicuspid  teeth   which   are   being   deflected   to 

the    lingual 157 

106.  Unerupted   biscup)id   teeth   which   are   rotated   and   erupting   to 

the    lingual 157 

107.  Eadiograms    showing   unerupted    cusj^id,    same    tooth    after    re- 

moval of  lateral  incisor  and  deciduous  cuspid,  showing  at- 
tachment for  moving  the  unerupted  tooth;  cuspid  tooth 
moved  down  to  the  point  of  eruption 158 

108.  Supernumerary    teeth.      Case    after    extraction 158 

109.  An  unerupted  lower  second  bicuspid  in  a  patient  twelve  years 

old 160 

110.  Unerupted  upjjcr  and  lower  bicuspids  in  a  patient  eleven  years 

of   age 160 

111.  Unerupted  cuspid  teeth  whose  relationship  to  the  roots  of  the 

incisors  must  be  taken  into  consideration  during  tooth 
movement 161 

112.  An  unerupted  lower  third  molar  which  is  crowding  the  incisors     162 

113.  An  erupting  lower  third  molar  which  has  been  responsible  for 

the  crowding  of  the  lower  incisors  and  cuspids     ....     162 

114.  Nonvital  tooth  being  used  as'  an'  anchor  tooth  and  nonvital  tooth 

which  was  not  considered  safe  for  anchorage     .     .     .     .     .     164 

115.  Supernumerary  upper   second  bicuspid 164 


ILLUSTRATIONS  15 

FIG.  PAGE 

116.  Lower   deciduous   central   incisors   having   the   appearance   of 

sui^ernumerary   teeth 164 

117.  Radiogram   showing   either   an   anomalous   central   incisor   or   a 

central  incisor  lying  in  a  horizontal  position  to  the  other 

teeth 164 

lis.     Patient   seated   and    tlie   apparatus    aiiangcd   to   make   a   radio- 
gram   of    the    left    side 165 

119.  Patient   seated   and  the  apparatus   airnngod  to   make   a   radio- 

gram of  the  right  side 165 

120.  An  x-ray  tube  inclosed  within  a  leaded  glass  tube  sliicld     .     .  172 

121.  Types  of  lead-lined  protection  screens 17.3 

122.  Lead-impregnated   glove 174 

123.  X-ray   protection   apron 175 


DENTAL  AND  ORAL  RADIOGRAPHY 


CHAPTER  I 

INTRODUCTION 

When  William  Conrad  Roentgen  announced  his  dis- 
covery to  the  world,  he  called  it  the  "x-ray,"  but  the  civ- 
ilized world  has  for  the  most  part  seen  fit  to  designate  it 
the  ''roentgen  ray"  in  honor  of  the  discoverer.  Roent- 
genology is,  therefore,  defined  as  "the  study  and  prac- 
tice of  the  roentgen  ray  as  it  applies  to  medicine  and 
surgery. ' ' 

For  purposes  of  study,  roentgenology  may  be  divided 
into  two  distinct  fields,  depending  upon  the  purpose  for 
which  the  roentgen  ray  is  to  be  utilized.  In  the  first, 
which  is  the  one  enlisting  the  interest  of  dentists,  it  is 
used  for  the  production  of  shadow  pictures  or  radio- 
grams. In  other  words,  it  embraces  what  is  commonly 
called  the  "field  of  radiography,"  or  "roentgenog- 
raphy. ' ' 

The  other  branch  mentioned  includes  the  use  of  the 
roentgen  ray  for  therapeutic  purposes,  and  is  known 
as  "radiotherapy,"  or  "roentgenotherapy."  With  this 
field,  the  dentist  is  happily  not  directly  concerned,  and, 
therefore,  his  responsibilities  are  not  so  great  as  the 
medical  roentgenologist. 

Of  the  various  collateral  sciences  of  medicine,  there  is 
no  other  which  has  developed  more  rapidly,  or  which  has 
assumed  a  more  important  bearing  in  many  branches  of 
practice  than  has  the  science  of  roentgenology.  With  the 
increased  appreciation  of  its  value,  and  its  wide  adop- 

17 


18  DENTAL   AND    ORAL   RADIOGRAPHY 

tion,  it  has  been  developed  through  a  comparatively 
short  period  of  evolution,  until  now  it  can  be  regarded, 
broadly  S]3eaking,  in  the  light  of  an  exact  science. 

In  spite  of  this  fact,  there  is  still  apparent  a  great  de- 
gree of  misconception  as  to  the  responsibilities  of  one 
who  is  to  actively  engage  in  this  work. 

To  the  uninitiated,  this  field  of  labor  often  presents 
alluring  possibilities,  and  they  are  all  too  apt  to  rush 
in  without  adequate  preparation.  To  such,  the  reward 
of  bitter  disappointment  must  eventually  come,  when  they 
become  mired  in  the  mud  of  their  own  poor  judgment  and 
lack  of  technical  knowledge. 

To  avoid  such  an  end,  or  perhaps  what  is  almost  as 
ignominious, — the  acquiring  of  "a  partial  knowledge" 
of  the  subject,  which  at  best  can  only  carry  one  half- 
way upon  the  journey  of  success — the  student  should 
first  come  to  a  realization  that  the  practice  of  roentgen- 
ology or  any  of  its  branches,  requires  more  than  a  mere 
training  in  the  mechanics  of  the  x-ray  laboratory. 

Undoubtedly,  many  a  man  has,  in  the  contemplation  of 
x-ray  apparatus  for  his  office,  given  serious  thought  to 
the  type  of  equipment  ivhich  he  ivished  to  install,  and  has 
assumed  that  with  a  modern  laboratory,  he  would  be  in 
a  position  to  render  the  best  of  service.  Such  a  mis- 
guided individual  all  too  soon  learns  that  a  very  large 
part  of  the  battle  lies  ivithin  himself,  and  if  his  own 
knowledge  is  deficient,  the  finest  equipment  in  the  world 
will  not  make  him  a  roentgenologist. 

It  is  important,  therefore,  that  those  who  contemplate 
any  indulgence  in  the  field  of  radiography  should  not 
underestimate  the  task  that  confronts  them. 

In  addition  to  becoming  familiar  with  the  electro- 
physics  of  x-ray  laboratory  equipment,  its  practical  ap- 
plication in  his  chosen  field,  the  dangers  which  surround 
it  if  improperly  used,  one  should  realize  that  the  real 


INTRODUCTIOiSr  19 

practice  of  roentgenology  begins  when  the  x-ray  picture, 
or  radiogram,  has  been  produced.  It  is  quite  impos- 
sible for  such  an  image  to  be  of  value  unless  the  roent- 
genologist is  thoroughly  familiar  with  the  anatomy,  phys- 
iology, and  pathology  of  the  field  under  examination; 
and  even  these  qualifications  are  not  adequate  unless 
backed  up  by  practical  clinical  experience. 

For  those  who  can  qualify,  there  is  a  real  field  and  a 
rare  opportunity,  and  it  will  be  found  that  every  man 
who  engages  in  this  work  will  receive  just  that  amount 
of  recognition  and  respect  from  his  colleagues  to  which 
his  abilities  entitle  him. 

One  of  the  first  things  which  the  beginner  should  do 
is  to  become  familiar  with  the  terminology  of  this  sub- 
ject, and  cultivate  the  habit  of  using  terms  correctly. 
Instead  of  using  the  term  ''x-ray  picture,"  such  an  image 
should  always  be  spoken  of  as  a  "radiogram,"  or  as  a 
' '  roentgenogram. ' ' 

The  physician  or  the  dentist  maintaining  an  x-ray  lab- 
oratory should  not  be  called  ''an  x-ray  specialist,"  but 
should  be  spoken  of  as  "a  medical  or  a  dental  roent- 
genologist." 

Not  infrequently,  we  hear  physicians  or  dentists  speak- 
ing of  a  dental  radiogram  as  a  "dental  x-ray."  Such  an 
expression  only  exposes  their  crudity  of  thought,  and 
certainly  expresses  nothing  else. 

It  is  thought  by  some  terminologists  that  in  addition  to 
always  speaking  of  the  x-ray  as  the  roentgen  ray,  in  honor 
of  the  man  who  discovered  it,  we  should  include  the  name 
roentgen  in  every  descriptive  word  connected  with  the 
work.  To  such,  the  term  "radiograph"  (verb)  and 
"radiogram"  (noun)  will  doubtless  appear  improper, 
but  the  author  feels  justified  in  continuing  their  use,  as 
these  words  are  thoroughly  descriptive  and  less  cum- 
bersome than  "roentgenograph"  and  "roentgenogram." 


20 


DENTAL   AlsTD    ORAL   RADIOGRAPHY 


For  the  same  reason,  the  term  ''radiography"  is  pre- 
ferred rather  than  "roentgenography"  to  designate  the 
art  of  making  radiograms. 

Briefly  summarized,  the  following  roentgen  terminol- 
ogy will  be  found  to  be  quite  adequate : 


Roentgen  ray,  or 
X-ray : 

Roentgenology,  or 
Radiology:^ 

Roentgenologist,  or 
Radiologist :  * 


A  phenomenon  in  physics  discovered  by 
William   Conrad  Roentgen. 


The  study  and  practice  of  the  roentgen 
ray  as  applied  to  medicine  and  surgery. 

One  skilled  in  roentgenology,  or  radi- 
ology. 

The  shadow  picture  produced  by  the  x- 
ray  upon  the  photographic  emulsion. 

(Verb.)  To  make  a  roentgenogram,  or 
radiogram. 

The  art  of  making  roentgenograms,  or 
radiograms. 

Treatment  by  the  application  of  the 
roentgen  ray. 

Skin  reaction  due  to  too  strong  or  too 
often  repeated  application  of  the  roent- 
gen ray. 

Roentgenographic  examination,  or    The  examination  and  study  of  the  shadow 


Roentgenogram,  or 
Radiogram : 

RoentgenograjDh,  or 
Radiograph : 

Roentgenography,  or 
Radiography : 

Roentgenotherapy,  or 
Radiotherapy : " 

Roentgen  dermititis,  or 
X-ray  dermatitis : 


Radiographic  examination : 

Roentgen  diagnosis,  or 
X-ray  diagnosis: 
Pathoroentgenography,  or 
Pathoradiography :  t 


pictures   produced   by   the  x-ray   upon 
the  photographic  emulsion. 

Diagnosis  by  aid  of  the  roentgen  ray. 

Tlie  study  of  pathologic  lesions  as  re- 
vealed by  the  radiogram,  or  roentgeno- 
gram; it  implies  and  renders  impera- 
tive a  knowledge  of  the  pathology  and 
of  the  interpretation  of  normal  and 
abnormal  tissue  densities  as  recorded 
in  the  radiogram. 

To  apply  the  roentgen  ray. 

The   application   of  the  roentgen   ray. 

The  untoward  effect  of  the  roentgen  ray. 

*The  term  is  rather  confusing,   as  it   could   also   refer   to   the  practice   and   therapy 
of  radium  or  other  radiotherapeutic  agents. 
tTerms  suggested  by  Dr.  Julio  Endelman. 


Roentgenize : 
Roentgenization : 
Roentgenism : 


INTRODUCTIOIT  21 

Some  writers  add  other  descriptive  terms  to  the  fore- 
going list,  but  the  author  feels  that  a  terminology  should 
be  just  as  brief  as  is  consistent  with  adequate  descrip- 
tion ;  hence,  several  terms  appearing  in  current  literature 
on  different  phases  of  roentgenology  have  been  omitted. 


CHAPTER  II 

THE  NATURE  OF  THE  X-RAY  AND  ITS 
DISCOVERY 

In  order  to  gain  an  intelligent  conception  of  the  x- 
ray,  it  is  quite  necessary  tliat  the  student  start  mth 
a  consideration  of  certain  phases  of  electrophysics,  and 
radiant  energy,  or  in  fact  the  very  foundation  of  matter 
itself. 

According  to  the  most  plausible  theories  and  beliefs, 
all  matter  is  suspended  or  contained  in  the  medium 
knoA\Ti  as  ether,  which  is  an  elastic  medium  filling  all 
space,  interatomic  and  interelectronic,  as  well  as  all 
other  space  of  which  we  have  any  knowledge. 

Furthermore,  many  facts  brought  out  by  the  close 
study  of  chemistry  and  physics  seem  to  justify  the  be- 
lief that  all  substances  of  matter  are  composed  of  mi- 
nute particles  called  "molecules,"  and  that  each  mole- 
cule is  made  up  of  two  or  more  elements  called  "atoms," 
while  these  atoms  are  also  further  divided  in  particles 
knoAvn  as  electrons. 

These  electrons,  or  units  of  matter,  are  never  still,  but 
are  in  a  constant  state  of  motion  or  vibration,  each  sub- 
stance having  its  OA\m  specific  atom  and  the  electrons  of 
such  atoms  having  their  own  rate  of  vibration. 

The  vibration  of  these  electrons  produces  disturbances 
in  the  ether  kno^^t  as  ' '  ether  waves ' '  which  var}^  in  length 
according  to  the  rate  at  which  electrons  are  vibrating. 
If  the  rate  of  vibration  of  the  electrons  be  changed  or 
disturbed,  there  is  a  change  in  the  ether  waves,  resulting 
in  a  corresponding  change  in  the  phenomenon  produced. 

If  this  theory  of  matter  is  correct,  as  the  evidence  of 

22 


NATURE    OF    X-RAY   AND    ITS    DISCOVERY  23 

modern  science  would  lead  ns  to  believe,  all  matter  then 
is  made  up  of  the  same  constituents,  and  its  various  forms 
are  determined,  not  by  any  essential  difference  of  com- 
position, but  by  the  number,  arrangement  and  amount 
of  motion  of  the  ultimate  particles  making  up  the  atom. 

All  this  has  a  practical  significance  to  us  in  under- 
standing the  phenomenon  which  we  call  the  x-ray.  As 
stated  before,  it  is  known  that  a  certain  rate  of  vibra- 
tion of  electrons  will  produce  other  waves  resulting  in  a 
definite  phenomenon,  while  a  change  in  this  rate  will 
produce  an  entirely  different  phenomenon.  For  instance, 
a  slow  rate  of  vibration  (75,000,000  per  second)  produces 
what  are  known  as  electromagnetic  waves.  A  little 
higher  up  the  scale  where  the  electrons  are  made  to  vi- 
brate faster,  heat  waves  appear.  Another  increase,  and 
light  waves  appear.  If  we  continue  to  accelerate  the 
rate  of  vibrations  of  the  electrons,  there  will  be  pro- 
duced successively  ultra-violet,  or  Finsen  rays ;  then  cath- 
ode, or  radium,  rays,  and  finally  the  x-ray. 

It  will  then  be  seen  that  the  x-rays  are  produced  as  the 
result  of  the  most  rapid  rate  of  vibration  of  which  we 
have  any  knowledge.  In  the  laboratory  this  phenomenon 
is  produced  by  the  sudden  stopping  of  a  stream  of  rapidly 
moving  free  electrons  in  a  vacuum  tube  which  has  been 
exhausted  to  one  millionth  of  an  atmosphere. 

The  x-ray,  therefore,  may  he  defined  as  that  form  of 
radiation  ivhich  emanates  from  a  highly  exhausted  tube 
ivhen  an  electric  current  of  high  tension  is  passed  through 
the  tube.  The  object  of  the  vacuum  tube  is  to  establish 
a  medium  in  which  all  source  of  resistance  is  removed, 
so  that  the  electric  current  may  excite  the  exquisitely 
rapid  vibrations  necessary  to  produce  the  phenomenon 
desired,  the  electric  current  being  the  source  of  excita- 
tion. 

The  radiation  thus  produced  gives  neither  heat  nor 


24 


DEXTAL    AND    ORAL    RADIOGIIAPHY 


liglit,  nor  can  it  be  deflected,  reflected,  or  polarized.  In 
fact,  it  can  only  be  recognized  by  its  effect  npon  the 
photographic  plate  and  npon  such  chemicals  as  willem- 
ite,  calcinm,  and  tnngstate,  which  fluoresce  or  glow  un- 
der its  influence. 

The  Discovery  of  the  X-ray 

The  x-ray  was  discovered  in  1895  by  William  Conrad 
Roentgen,  Professor  of  Physics,  at  the  Eoyal  University 


Fig.    1. — William   Conrad   Roentgen. 


of  AViirzbnrg,  in  Germany.  This  discovery,  marking  as 
it  did,  a  distinct  epoch  in  the  science  of  medicine,  was  re- 
ceived by  the  world  with  incredulity  and  amazement,  for 


NATURE    or    X-RAY   AND    ITS    DISCOVERY 


25 


its  reported  possibilities  savored  almost  of  the  occult. 
"A  new  ray  had  been  discovered  by  means  of  which  it 
was  possible  to  look  through  opaque  substances." 

While  it  fell  to  the  lot  of  Professor  Eoentgen  to  make 
this  discovery,  there  is  no  doubt  but  that  other  experi- 
menters in  the  field  of  physics,  unconsciously  produced 
this  same  ray.  In  fact,  its  discovery  was  made  possible 
by  the  work  of  other  scientists  who  preceded  Roentgen 
and  laid  the  foundation  for  its  advent. 


Fig.  2. — Michael  Faraday. 


Of  these,  Michael  Faraday  was  the  pioneer.  In  1831 
he  discovered  electric  magnetic  induction,  which  made 
possible  the  induction  coil  and  the  other  electric  machines 


26 


DENTAL    AND    ORAL   RADIOGRAPHY 


utilized  to  generate  currents  of  great  potential.  As  early 
as  1838  he  conducted  a  series  of  experiments  to  deter- 
mine the  effect  of  electric  discharges  upon  rarified  gases, 
and  invented  the  terms  "anode"  and  "cathode"  for 
positive  and  negative  electrodes. 

In  1857  Geisgler  constructed  Jhe  Jir st  vacuum  tubes 
and  it  was  noted  at  this  time  that  an  electric  discharge 
passed  through  these  tubes  would  produce  a  peculiar 


■iS^APiiSBT-'^'^  =';''.=''.' 


Fig.    3. — Sir   William    Crookes. 

gloAv  or  phosphorescence,  the  coloring  of  which  depended 
upon  the  character  of  the  rarefied  gas  contained  in  the 
tube.  This  phenomenon  became  known  as  "fluores- 
cence. ' ' 

A  few  years  later  (1860)  Professor  Hittorf,  a  cele- 
brated physicist  of  Miinster,  conceived  the  idea  of  ex- 
hausting the  Geissler  tube  to  a  higher  degree  of  vacuum 
and  found  as  a  result  an  increased  resistance  to  the  pass- 


NATURE    OF    X-RAY   AND    ITS    DISCOVERY 


27 


ing  of  the  electric  discharge,  and  that  the  color  of  the 
rarefied  gases  under  fluorescence,  varied  with  the  degree 
of  rarefication.  He  also  discovered  another  fact  which 
was  to  have  an  important  bearing  upon  the  work  of  later 
experimenters,  and  that  was  that  the  luminous  discharge 
in  a  Geissler  tube  could  he  deflected  by  a  magnet. 

The  important  work  of  these  early  experimenters  was 
followed  later  (1878)  by  Sir  William  Crookes,  who  suc- 


Fig.   4. — Heinrich  Hertz. 

ceeded  in  constructing  a  more  perfect  vacuum  tube,  that 
is,  one  that  could  be  exhausted  to  a  much  higher  degree 
of  vacuum.  With  these  improved  tubes,  Crookes  discov- 
ered that  with  a  sufficiently  high  vacuum  the  luminous 
glow  within  the  tube  disappeared,  and  demonstrated  that 
within  it  there  was  a  rectilinear  radiation  from  the 
cathode,  which  he  conceived  as  being  a  projection  of  par- 
ticles of  highly  attenuated  gas  at  exceedingly  high  veloc- 


Z8  DEN^TAL   AND    ORAL   EADIOGEAPHY 

ity.  To  this  radiation  lie  gave  the  name  ' '  cathode  rays, ' ' 
and  because  of  the  peculiar  behavior  of  gas  in  this  ex- 
ceedingly rarefied  state,  he  concluded  that  it  was  as  dif- 
ferent from  gas  in  its  properties  as  ordinary  air  or  gas 
is  different  from  a  liquid.  He  found  that  the  impact  of 
the  cathode  rays  against  the  wall  of  the  tube  would  pro- 
duce within  it  a  greenish  "phosphorescence"  or  "fluores- 
cence" and  an  increase  in  temperature;  also  that  these 
rays  could  be  intercepted  by  metallic  plates  within  the 
tube.  By  concentrating  the  rays  at  the  focus  of  a  con- 
cave cathode,  he  was  able  to  produce  a  brilliant  fluores- 
cence and  a  very  high  temperature,  both  at  the  walls  of 
the  tube  and  in  various  substances  within  it.  Without 
doubt,  Sir  William  Crookes  unconsciously  produced  the 
x-ray  in  the  course  of  these  experiments. 

In  1892  Professor  Heinrich  Hertz  discovered  that 
cathode  rays  would  penetrate  gold  leaf  and  other  thin 
sheets  of  metal  placed  within  the  tube.  Soon  after  this 
discovery,  Hertz  died,  and  his  experiments  were  con- 
tinued by  his  assistant,  Lenard,  who  was  able  to  demon- 
strate that  many  of  the  phenomena  of  the  cathode  rays 
could  be  observed  outside  of  the  Crookes  tube.  By  clos- 
ing a  vacuum  tube  at  the  end  opposite  the  cathode  with 
a  thin  sheet  of  aluminum,  he  demonstrated  that  a  radia- 
tion proceeded  through  or  from  the  aluminum  walls  of 
the  tube  which  would  pass  through  many  substances 
opaque  to  ordinary  light,  and  after  passing  through  such 
substances,  it  would  excite  fluorescence  in  crystals  of  ba- 
rium platino-cyanide,  and  would  affect  sensitive  photo- 
graphic plates  in  much  the  same  manner  as  ordinary 
light.  Lenard  considered  that  all  these  phenomena  were 
due  to  the  cathode  rays  alone,  although  in  the  light  of 
our  present  knowledge,  there  is  no  doubt  that,  not  only 
in  his  experiments,  but  in  those  of  Crookes,  Hertz,  and 
other  investigators,  x-rays  were  produced.     However, 


NATURE    OF    X-RAY   AND    ITS    DISCOVERY  29 

they  were  not  recognized  as  such  until  1895,  when  Pro- 
fessor Roentgen  startled  the  world  hj  the  announcement 
of  his  discovery. 

Upon  the  memorable  day  of  his  discovery,  Professor 
Roentgen  was  duplicating  one  of  Lenard's  experiments 
in  the  laboratory  of  the  Wiirzburg  University.  The  ex- 
periment consisted  of  passing  an  electric  current  through 
a  Crookes  tube  covered  with  black  cardboard,  to  test  its 
fluorescence  upon  a  piece  of  cardboard  coated  A\dth  ba- 
rium platino-cyanide.  A  fresh  specimen  of  this  chemical 
had  been  prepared  and  spread  upon  the  cardboard  which 
was  placed  against  the  wall  on  the  opposite  side  of  the 
room  to  dry.  The  room  was  darkened  and  the  current 
was  passing  through  the  tube,  when  to  his  amazement. 
Roentgen  noticed  that  the  chemically  covered  cardboard 
on  the  other  side  of  the  room  was  glowing  with  a  wierd 
fl.uorescence.  He  approached  the  cardboard,  and  in  doing 
so,  passed  between  it  and  the  Crookes  tube,  and  beheld 
his  shadow  upon  the  cardboard.  Picking  up  a  book,  he 
held  it  in  front  of  the  screen  and  noticed  that  it  also  cast 
a  shadow.  He  then  discovered  that  the  luminous  glow  or 
fluorescence  on  the  cardboard  appeared  and  disappeared 
with  the  turning  on  and  off  of  the  current.  With  the 
tube  operating,  he  picked  up  the  cardboard,  and  while 
examining  it,  noticed  the  shadow  of  his  hand  on  its 
surface,  the  bones  appearing  much  darker  than  the  soft 
parts  of  the  hand.  He  also  found  that  the  fluorescence 
was  produced  in  the  cardboard  regardless  of  whether  the 
chemically  coated  side  was  turned  toward  or  away  from 
the  Crookes  tube,  showing  that  the  rays  had  the  power 
to  penetrate  substances  at  a  distance  from  the  tube. 

Further  investigation  proved  that  the  radiation  pro- 
ducing these  phenomena  emanated  from  the  point  of  im- 
pact of  the  cathode  rays  against  the  glass  wall  of  the 
Crookes  tube;  that  nearly  all   substances  were  trans- 


30  DENTAL   AjSTD    OKAL   RADIOGRAPHY 

parent  to  it,  although  in  widely  different  degrees,  varying 
roughly  with  their  density ;  that  the  radiation  was  recti- 
linear; that  it  could  not  be  refracted,  reflected,  or  de- 
flected by  a  magnet.  Hence  it  was  plain  to  Roentgen  that 
these  rays  were  quite  different  from  the  cathode  rays  of 
Crookes,  Hertz,  or  Lenard. 

Using  photograiDhic  plates  wrapped  in  black  paper  to 
protect  them  from  ordinary  light,  he  obtained  with  these 
new  rays  shadow  pictures  of  metallic  objects  in  a  wooden 
box,  and  of  the  bones  of  the  hand. 

He  continued  his  experiments  both  with  the  fluorescent 
screen  and  the  photographic  plate,  and  in  December, 
1895,  communicated  his  discovery  to  the  Physico-Medical 
Society  of  Wiirzburg.  Being  unable  to  determine  the 
exact  nature  of  this  new  ray  other  than  classing  the 
phenomenon  as  longitudinal  vibrations  of  ether.  Roent- 
gen called  it  the  x-ray,  the  letter  "x"  representing  the 
unknown  in  the  mathematical  formula.  Even  today  the 
exact  nature  of  the  rays  has  not  been  determined,  al- 
though the  concensus  of  opinion  seems  to  be  that  they 
are  violent  ether  pulses  set  up  by  the  sudden  stoppage 
of  the  cathode  rays  as  they  strike  upon  the  walls  of  the 
tube  or  upon  any  intervening  obstruction.  If  this  theory 
be  correct,  x-ra^^s  are  of  the  same  general  nature  as  light 
waves,  but  of  such  short  wave  length  that  they  lie  out- 
side the  visible  spectrum. 


CHAPTER  III 

HIGH  TENSION  ELECTRIC  CURRENTS- 
MAGNETISM— ELECTROMAGNETIC 
INDUCTION 

High  Tension  Electric  Currents 

As  stated  previously,  the  x-ray  is  produced  Avhen  an 
electric  current  of  high  tension  is  passed  through  a  vac- 
uum tube.  Therefore,  let  us  consider  the  character  of 
this  current  and  the  means  employed  to  produce  it. 

There  are  several  kinds  of  electric  currents,  but  of 
these  we  need  concern  ourselves  only  with  two — the 
direct  current,  commonly  designated  by  the  abbreviation 
D.C. ;  and  the  alternating  current,  designated  as  A.C. 

The  direct  current  is  one  in  which  the  electricity  flows 
along  a  conductor  in  one  direction  at  a  uniform  rate  of 
pressure,  while  the  alternating  current  flows  along  a  con- 
ductor first  in  one  direction,  then  reverses  and  flows  in 
the  opposite  direction,  these  changes  taking  place  with 
great  rapidity  (50  to  120  per  second).  Such  a  current  in 
making  these  changes  is  said  to  have  completed  a  cycle, 
and  its  frequency  is  designated  by  the  number  of  alter- 
nations which  occur  each  second. 

A  high  tension  current  is  one  which  has  high  voltage, 
or,  as  it  is  expressed  in  electrical  terms,  has  great  elec- 
tromotive force,  or  pressure. 

The  Volt  is  defined  as  the  unit  of  electromotive  force, 
and  is  analogous  to  the  pressure  caused  by  a  difference 
in  level  of  two  bodies  of  water  connected  by  a  pipe — the 
pressure  tends  to  force  the  water  through  the  pipe  and 


32  DENTAL   AED    ORAL   RADIOGRAPHY 

the  electromotive  force  or  voltage  tends  to  cause  the  elec- 
tric current  to  flow  along  a  conductor. 

The  Ampere  is  the  unit  of  current  strength,  or  in  other 
words,  the  amount  of  current  passing  a  given  point  on  a 
conductor  in  a  given  time.  If  Ave  again  use  the  analogy 
of  the  two  bodies  of  water  at  different  levels  connected 
by  a  pipe,  it  would  be  the  amount  of  water  which  could 
pass  through  the  pipe  in  a  given  time. 

The  0]i7n  is  the  unit  of  resistance.  Just  as  the  water 
in  flowing  through  a  pipe  is  resisted  somewhat  in  its  pas- 
sage by  the  friction  offered  by  the  surface  of  the  pipe, 
or  by  the  limited  capacity  of  the  pipe,  so,  likewise,  the 
electric  current  is  resisted  in  varying  degrees  in  its  pas- 
sage along  a  conductor,  the  degree  of  resistance  depend- 
ing upon  the  degree  of  conductivity  of  the  material  used 
as  the  conductor,  its  length,  cross  section,  etc. 

The  Watt  is  the  unit  of  electromotive  powder  or  the 
ability  of  a  current  to  do  work.  The  wattage  of  a  cur- 
rent is  determined  by  the  voltage,  or  pressure,  and  the 
amperage  or  quantity,  the  wattage  of  a  given  current  be- 
ing determined  by  multiplying  the  voltage  by  the  am- 
perage. 

From  the  foregoing,  then,  we  see  that  the  character  of 
an  electric  current  is  determined  by  several  factors,  all 
of  which  must  be  taken  into  consideration. 

If  we  wish  to  know  the  strength  of  a  given  current,  we 
have  but  to  remember  this  strength  will  depend  upon  the 
pressure  or  electromotive  force  and  the  resistance  of- 
fered by  the  conductor  through  which  the  current  is  pas- 
sing, just  as  the  strength  of  a  stream  of  water  flowing 
from  a  tank  would  depend  upon  the  pressure  and  the  size 
*>jOf  the  pipe  carrying  the  water.  In  other  words,  the 
strength  of  the  electric  current  equals  the  pressure  di- 
vided by  the  resistance.  Reducing  this  to  an  equation 
we  have — 


HIGH    TENSION    ELECTRIC    CURRENTS  33 

voUs                           E.M.F. 
Amperes  =     ^^^^^    or  C  equals  —^ 

This  is  known  as  "Olim's  Law"  and  is  one  of  the  fun- 
damental laws  upon  which  electrical  science  is  based. 
This  important  law  has  two  other  forms  which  make  it 
possible  to  learn  the  relationship  and  amount  of  any  of 
these  three  units,  provided  two  are  knoAvn.  For  instance, 
by  transposing  the  formula  of  Ohm's  law,  we  have — 

Volts  =  amperes  x  ohms,  or  E.M.F.  :=  C  x  R. 

If  we  wish  to  determine  the  resistance  offered  b)^  a 
given  conductor,  we  apply  the  formula  as  follows : 

E.M.F.  E.M.F. 

Resistance  = or  R  = z^ 

amperage  U 

As  stated  before,  the  current  which  is  passed  through 
the  vacuum  tube  to  generate  the  x-rays  must  be  a  cur- 
rent of  high  tension,  or  great  pressure ;  or,  expressed  in 
the  terms  of  the  units  just  described,  it  must  have  very 
high  voltage.  The  ordinary  lighting  current  of  110  volts 
is  inadequate,  as  this  current  is  of  far  too  low  potential 
to  pass  through  the  tube,  as  the  vacuum  offers  great  re- 
sistance, a  resistance  which  to  the  ordinary  current 
amounts  to  an  absolute  nonconductor.  AVe  are  obliged, 
therefore,  to  make  use  of  some  means  which  mil  pro- 
duce a  current  of  great  voltage,  a  current,  we  will  say, 
of  at  least  75,000  to  150,000  volts. 

To  do  this,  we  must  make  use  of  one  of  the  electric 
machines  which  can  generate  such  a  current  by  utilizing 
the  principle  of  electromagnetic  induction.  Lest  the  stu- 
dent become  confused,  we  will  first  review  very  briefly 
some  of  the  elementary  principles  of  electromagnetism 
and  its  relation  to  the  production  of  the  high  tension  cur- 
rent necessary  in  x-ray  production. 


34  DENTAL   AND    ORAL    RADIOGRAPHY 

Magnetism 

Magnetism  is  the  term  applied  to  substances  which 
have  the  property  of  attracting  small  pieces  of  iron.  A 
material  possessing  this  property  was  first  foimd  by  the 
ancients  at  Magnesia,  in  Asia  Minor,  from  which  fact 
arose  the  name  magnet. 

The  natural  magnet  is  an  oxide  of  iron  and  is  also 
called  the  lodestone.  Artificial  magnets  can  be  made  by 
rubbing  a  bar  of  hard  steel  with  a  lodestone,  or  with  an- 
other artificial  magnet,  or  by  means  of  an  electric  cur- 
rent. Artificial  magnets  acquire  the  same  magnetic 
properties  Avhich  the  lodestone  or  natural  magnet  pos- 
sesses except  that  they  acquire  them  to  a  much  greater 
extent,  and  are,  therefore,  always  used  in  preference  to 
natural  magnets. 

In  addition  to  the  property  of  attracting  small  pieces 
of  iron,  magnets  have  other  characteristics  worthy  of 
mention,  such  as  polarity,  or  the  property  of  assuming, 
when  suspended  and  perfectly  free  to  move,  a  north  and 
south  position.  The  compass  is  quoted  as  a  familiar 
example. 

At  the  ends  of  a  magnet,  or  in  other  words  at  its  poles, 
the  greatest  power  or  attraction  exists.  This  is  easily 
illustrated  by  placing  one  end  of  an  ordinary  magnet  in 
some  iron  filings  and  withdramng  it.  The  filings  will 
cling  to  it  in  great  numbers,  as  they  will  likewise  do  to 
the  other  end  of  the  same  magnet  if  it  too  be  placed  in 
the  filings.  The  middle  of  the  magnet  (or  that  portion 
midway  between  the  two  poles),  however,  does  not  pos- 
sess this  property;  but  as  the  ends  are  approached,  the 
attraction  increases  until  the  poles  are  reached,  where  it 
reaches  the  maximum. 

In  observing  the  action  of  the  two  poles  of  a  magnet 
in  attracting  the  iron  filings,  no  particular  difference  is 


HIGH    TEXSTON    ELECTRIC    CURREXTS 


6.} 


observed.  They  both  attract  the  iron  filings.  There  is  a 
difference,  however,  which  may  he  shown  l)}^  experiment- 
ing with  two  magnets,  one  of  which  should  be  suspended 
at  its  center  like  an  ordinary  compass,  while  the  other  is 
held  in  the  hand.  If  the  north  pole  of  the  magnet  held 
in  the  hand  is  moved  near  the  north  pole  of  the  sus- 
pended magnet,  they  ivill  repel  each  other.  Likewise  if 
their  south  poles  are  approached,  they  will  repel  each 
other.  But  if  the  north  pole  of  one  be  placed  near  the 
south  pole  of  the   other,  they  will  attract  each  other. 


Fig.  5. — The  action  of  iron  filings  in  forming  definite  curved  lines  about  an  or- 
dinary bar  magnet  indicates  that  the  magnetic  field  exerts  its  influence  in  certain 
definite   directions   which   are   called   "the   magnetic   lines   of  force.'"' 


This  shows  that  like  poles  repel  each  other,  ivhile  unlike 
poles  attract  each  other. 

The  space  surrounding  a  magnet  which  is  subject  to 
its  influence  is  known  as  its  magnetic  field.  The  presence 
of  this  magnetic  field  is  easily  demonstrated  by  placing  a 
magnet  under  a  sheet  of  paper  upon  which  iron  filings 
have  been  evenly  spread.  By  tapping  the  paper  lightly, 
the  filings  will  form  into  a  series  of  curved  lines  extend- 
ing from  one  pole  of  the  magnet  to  the  other  pole,  as  il- 
lustrated in  Fig.   5.     The  formation   of  these  definite 


36  DENTAL    AND    ORAL   RADIOGRAPHY 

curves  indicates  that  the  magnetic  field  exerts  its  influ- 
ence in  certain  definite  directions  which  are  called  the 
lines  of  magnetic  force.  These  lines  of  force  start  at  one 
IDole  of  the  magnet,  pass  in  curved  lines  around  to  the 
opposite  pole,  where  they  re-enter  and  pass  on  through 
the  magnet  again,  so  that  if  any  line  is  followed  through 
its  entire  length,  one  will  eventually  come  back  to  the 
starting  point,  as  shown  in  Fig.  6. 

It  is  by  virtue  of  its  magnetic  field,  that  a  magnet  has 
the  power  of  attracting  pieces  of  iron.    A¥hen  a  piece  of 

'11/^' ^^    \       \    \    \ 

>  \  \\\     '  '  ,,////// 

\  ^  \\s  \  M  /  /  /  //^^/ 


\    \      \      \         "-^  ^^       /       I     \     ^ 

Fig.   6. — Diagrammaiic  illustration   of  the  magnetic  lines  of  force. 

iron  is  brought  under  its  influence,  it  becomes  a  tem- 
porary magnet,  and  for  the  time  being  has  its  two  poles. 
If  the  north  pole  of  a  magnet  is  brought  close  to  a  piece 
of  iron,  a  south  pole  will  be  induced  in  the  iron  next  to 
this  north  pole,  and  a  north  pole  in  the  portion  farthest 
from  it.  The  attraction  is  then  exactly  similar  to  the  at- 
traction between  two  permanent  magnets  when  two  un- 
like poles  are  brought  together.  This  action  of  a  mag- 
net in  developing  magnetism  in  iron  placed  in  its  mag- 
netic field  is  called  magnetic  induction. 

When  a  piece  of  iron  is  in  contact  with  a  magnet,  the 
attraction  is  greatest;  but  actual  contact  is  unnecessary 


HIGH    TENSION    ELECTRIC    CURRENTS  6( 

to  magnetize  the  iron,  as  it  need  only  be  placed  within 
the  magnetic  field,  or,  in  other  Avords,  within  the  mag- 
netic lines  of  force  of  the  magnet. 

Magnetism  may  be  induced  in  iron  in  another  way  not 
yet  described,  and  to  us  this  is  of  great  importance.  If 
an  ordinary  electric  current  is  passed  through  a  coil  of 
wire,  the  coil  becomes  equivalent  to  a  magnet  and  is  sur- 
rounded by  a  magnetic  field  similar  to  that  of  a  bar  mag- 
net. Such  a  coil  of  Avire  is  called  a  helix,  and  if  its 
length  is  many  times  its  diameter,  it  is  called  a  solenoid. 


/  ^  .^  ^^    \  \ 


Fig.    7. — Diagrammatic    illustration    of   the    magnetic    field    surrounding    a   coil    of    wire 
through   which   an   electric   current  is   passing. 

Since  a  solenoid  is  surrounded  by  a  magnetic  field  sim- 
ilar to  that  of  a  magnet  (see  Fig.  7)  it  follows  that  a 
solenoid  is  capable  of  magnetizing  pieces  of  soft  iron 
and  attracting  them  in  the  same  Avay  as  does  an  ordinary 
steel  magnet.  The  magnetic  field  of  a  solenoid  is 
strongest  Avithin  its  Avindings  and  therefore  if  a  bar  of 
soft  iron  is  placed  Avithin  the  coil,  the  bar  ayIII  be  much 
more  strongly  magnetized  than  if  placed  in  any  other 
position  about  the  coil.  Such  a  coil  adapted  to  carry  a 
current  and  provided  Avith  a  soft  iron  bar  or  core  is 
called  an  electromagnet  (Fig.  8). 


do  DENTAL   AND    ORAL   EADIOGRAPHY 

In  order  to  permit  the  wire  to  be  closely  wound  and 
at  the  same  time  to  allow  the  current  to  pass  through 
each  turn,  the  wire  must  be  covered  with  insulation 
throughout  its  length.  It  should  also  be  remembered 
that  the  iron  core  witliin  the  solenoid  remains  a  magnet 
only  ivMle  the  current  is  passing  through  the  coil,  as 
"only  electric  charges  in  motion  produce  magnetic 
effects." 

Electromagnets  are  much  more  powerful  than  ordinary 
magnets;  that  is,  their  fields  have  much  greater  strength, 


Fig.   8. — An  iron  bar  placed   within  the  windings   of  a  solenoid   is  subject   to   its   mag- 
netic field   and   becomes   a   magnet. 

for  the  field  of  the  electromagnet  is  equal  to  the  sum  of 
the  field  due  to  the  core,  plus  the  field  due  to  the  current 
passing  through  the  coil. 

Thus  far  we  have  discussed  the  fact  that  a  magnetic 
substance  in  the  field  of  an  ordinary  magnet,  or  a  con- 
ductor carrying  an  electric  current,  is  magnetized.  This 
phenomenon,  we  know,  is  due  to  magnetic  induction.  It 
is  also  a  fact  that  an  electric  current  may  he  induced  in 
a  conductor  hy  causing  the  latter  to  move  through  a  mag- 
netic field.  It  makes  no  difference  whether  this  field 
comes  from  an  ordinary  magnet  or  from  an  electric 
charge  passing  through  a  conductor.     This  action  of  a 


HIGH    TENSION    ELECTRIC    CURRENTS  6.) 

magnet  or  of  a  current  on  a  conductor  moved  in  its  field 
is  called  electromagnetic  induction. 

Principles  of  ElectromagTietic  Induction 

If  the  ends  of  a  coil  of  wire  are  connected  with  a  gal- 
vanometer (Fig.  9)  and  the  coil  is  moved  down  over  an 
ordinary  magnet,  the  galvanometer  will  show  that  a  mo- 
mentary electric  current  has  passed  through  the  coil. 
The  current  continues  as  long  as  the  coil  is  in  motion, 


Fig. 


9. — A,   magnet   with   diagrammatic   illustration   of   "magnetic   lines   of   force"    sur- 
rounding it.     B  shows  a  coil  of  wire  connected  to  a  galvanometer,  C. 


and  ceases  as  soon  as  the  coil  is  brought  to  rest.  If  the 
coil  is  withdrawn  from  the  magnet,  a  current  is  also  in- 
duced which  flows  in  an  opposite  direction  to  the  current 
which  was  induced  when  the  coil  was  carried  down  over 
the  magnet. 

These  induced  currents  are  produced  hy  the  field  sur- 
rounding the  magnet  moving  or  cutting  across  the  ivires 
composing  the  coil.  If  a  current  is  passed  through  the 
coil,  it  creates  a  magnetic  field,  and,  on  the  other  hand. 


40 


DENTAL   AND    OEAL   EADIOGRAPHY 


the  movement  of  a  magnetic  field  within  the  coil  produces 
a  current. 

As  a  solenoid  is  surrounded  by  a  magnetic  field  similar 
to  an  ordinary  bar  magnet,  it  follows  that  if  a  solenoid 
carrying  a  current  were  thrust  within  (Fig.  10)  another 
coil,  induced  currents  will  be  produced  in  the  latter. 
These  induced  currents,  as  in  the  case  where  the  magnet 
is  used,  only  flow  while  there  is  a  relative  movement  be- 
tween the  magnetic  field  and  the  conductor.    When  the 


Fig.    10. — A,  battery   from   which   an   electric   current   is   passing  through   the   solenoid, 
B;   C,   large   coil   into   which  the  smaller  coil  B  is  passed;   D,  galvanometer. 

solenoid  is  passed  into  the  other  coil,  the  induced  cur- 
rent will  flow  in  an  opposite  direction  to  the  current 
fjOiuing  in  the  solenoid,  and  upon  tvithdrawing  the  sole- 
noid, the  induced  current  ivill  floiu  in  the  same  direction 
as  the  current  in  the  solenoid. 

Suppose  the  two  coils  just  described  are  jolaced  one 
mthin  the  other  (there  being  no  current  passing)  and 
while  in  this  position  a  current  is  started  in  the  inner 
coil.  Upon  the  passage  of  the  current  in  the  inner  coil, 
a  momentary  current  is  induced  in  the  outer  coil,  just  the 


HIGH    TENSION    ELECTRIC    CURRENTS  41 

same  as  if  a  magnet  had  been  moved  within  it,  as  sho-wn 
in  Fig.  9.  This  induced  current  remains  only  while  the 
current  in  the  inner  coil  is  increasing  in  value  from  zero 
to  its  normal  strength.  As  soon  as  this  normal  strength 
is  reached,  the  induced  current  ceases  to  flow.  Now  if 
the  circuit  of  the  inner  coil  is  broken  and  its  current 
ceases  to  flow,  at  this  instant  another  momentary  cur- 
rent is  induced  in  the  outer  coil,  which  flows  in  a  direc- 
tion opposite  to  the  current  Avhich  Avas  induced  by  start- 
ing the  current.  These  two  induced  currents  created  by 
starting  and  stopping  the  primary  current,  or  in  other 
words,  by  ''making"  and  ''breaking"  the  current,  are 
not  of  equal  strength,  the  one  produced  by  the  "hreah" 
of  the  current  being  much  the  stronger. 

Such  an  instrument  arranged  with  one  coil  within  the 
other,  but  without  any  connection  between  the  two  coils, 
is  known  as  an  "induction  coil."  The  inner  coil  which 
is  usually  supplied  with  an  iron  core,  is  kno^vn  as  the 
"primary  coil;"  and  the  outer  coil,  in  Avhich  the  current 
is  induced,  is  known  as  the  "secondary  coil." 

Induced  currents  are  greatly  intensified  when  soft  iron 
cores  are  placed  within  the  primary  coils,  as  the  cores 
become  magnets  and  increase  the  strength  of  the  field 
by  adding  largely  to  the  lines  of  force  therein. 

If  an  induction  coil  is  constructed  mth  the  same  num- 
ber of  turns  of  wire  in  the  "secondary"  as  are  present 
in  the  "primary,"  the  current  induced  in  the  secondary 
will  be  exactly  equal  to  the  current  passed  through  the 
primary.  The  voltage  ivill  not  he  increased.  On  the 
other  hand,  if  the  secondary  contains  twice  as  many 
turns  as  the  primary,  the  induced  current  will  be  double 
the  voltage  of  the  primary,  as  each  turn  of  the  secondary 
induces  a  current  in  the  turns  directly  adjacent  to  it, 
which  must  be  added  to  the  current  induced  in  the  first 
layer  by  the  action  of  the  primary  current.    Therefore, 


42  DENTAL    AND    ORAL   RADIOGRAPHY 

it  should  be  apparent  that  as  we  increase  the  number  of 
turns  in  the  secondary,  we  increase  the  E.M.F.,  or  volt- 
age. This  increase  of  E.M.F. ,  or  voltage,  is  due  to  the 
phenomena  of  "self-induction"  which  is  the  principle 
utilized  in  all  x-ray  machines  or  other  electrical  appara- 
tus used  to  ''step  up"  the  E.M.F.,  or  voltage. 


CHAPTER  IV 

X-EAY  MACHINES 

RHUMKORFF  OR  INDUCTION  COIL— TESLA 

OR  HIGH  FREQUENCY  COIL-INTERRUP- 

TERLESS  TRANSFORMER 

The  Rhumkorff  or  Induction  Coil 

The  Rhumkorff,  or  ''induction  coil,"  which  is  the  most 
common  type  of  x-ray  machine  in  use  today,  consists  of 
two  principal  parts,  each  of  which  is  a  coil  of  mre,  one 
being  contained  within  the  other,  although  they  have  no 
electrical  connection   (see  Fig.  11). 

The  inner  coil,  or  "primary,"  as  it  is  called,  consists 
of  a  few  turns  of  very  coarse  insulated  ^^ire  Avrapped 
about  a  bundle  of  soft  iron  which  is  knomi  as  "the  mag- 
netic core." 

The  outer  coil,  or  "secondary"  is  made  up  of  a  great 
many  turns  of  fine  insulated  wire.  It  has  been  estimated 
that  in  a  12-inch  induction  coil  the  secondary  coil  is 
wound  with  between  twenty  and  thirty  miles  of  wire. 
This,  of  course,  makes  possible  an  enormous  number  of 
' '  turns  of  wire ' '  so  that  when  we  consider  that  each  turn 
of  the  secondary  induces  a  current  in  the  turn  directly 
adjacent  to  it,  which  must  be  added  to  the  current  in- 
duced in  the  first  layer  by  the  action  of  the  primary  cur- 
rent, the  sum  total  of  the  current  coming  from  the  sec- 
ondary amounts  to  something  tremendous. 

To.  compute  the  E.M.F.,  of  the  induced  current  (or 
that  coming  from  the  secondary),  we  have  but  to  remem- 
ber that  "the  E.M.F.,  of  the  induced  current  is  to  that 
of  the  primary  current,  as  the  number  of  turns  in  the 


44 


DENTAL   AND    OKAL   RADIOGEAPHY 


Fig  11.— Diagrammatic  illustration  of  the  essential  parts  of  an  induction  coil. 
A'  and  A  are  the  terminals  of  the  "primary  coil."  D  represents  the  windings  ot^the 
"primary"  about  the  magnetic  core  C.  The  insulating  medium  between  ^^the  pri- 
mary" and  "secondary"  is  shown  at  E.  The  windings  of  the  "secondary  coil  are 
designated   by   F,   and   the   "secondary"    terminals   by   B   and  B' . 


X-RAY    MACHTI^TES  45 

secondary  coil  is  to  the  number  of  turns  in  tlie  primary." 
For  instance,  suppose  we  have  an  induction  coil  with  10 
turns  of  wire  in  the  primary,  and  100  turns  of  wire  in 
the  secondary.  If  we  pass  a  current  of  110  volts  through 
the  "primary,"  the  voltage  of  the  "secondary"  current 
will  be — 

110 
-Yq-xIOO^hIIOO  volts. 

Notwithstanding  the  great  change  in  voltage,  the  wat- 
tage of  the  secondary  current  is  the  same  as  it  was  in 
the  primary  (except  for  a  small  loss  due  to  internal  re- 
sistance). This  is  not  true,  however,  of  the  amperage. 
For  example,  if  the  primary  current  of  110  volts  carries 
5  amperes,  its  wattage  would  be  550.  The  wattage  of  the 
secondary  current  would  also  be  550,  and  since  wattage 
equals  amperes  multiplied  by  volts,  the  amperage  of  the 
secondary  current  would  be. 

550 
jj^  =  y-2   ampere. 

Thus  it  will  be  seen  that  as  the  voltage,  or  E.M.F.,  is 
increased  in  the  before  described  manner,  the  amperage 
or  current  strength  is  decreased  in  equal  ratio.  It  should 
be  plain,  therefore,  that  the  original  current  running  to 
the  primary  is  not  changed  in  actual  value,  but  is  sim- 
ply transformed  to  a  state  or  condition  where  it  will  do 
the  special  work  required  of  it. 

In  our  consideration  thus  far  we  have  considered  the 
manner  in  which  an  electric  current  may  be  transformed 
from  a  low  to  the  high  voltage  necessary  to  energize  an 
x-ray  tube.  We  have  not,  however,  named  one  important 
requisite  of  a  current  to  be  used  for  this  purpose,  namely, 
that  the  current  must  flow  continuously  and  in  the  same 
direction. 

In  considering  the  manner  of  obtaining  a  current  in 


46 


dejsttal  and  oral  radiography 


the  secondary,  we  learned  that  such  a  current  is  produced 
by  "making"  and  ' ' brealdng "  the  primary  current.  If 
a  continuous  current  is  to  be  kept  flowing,  we  must  utilize 
some  instrument  which  will  rapidly  ' '  make ' '  and ' '  break ' ' 
the  current  in  the  primary  circuit.  Such  an  instrument 
is  knoA^m  as  an  "  interrupter ' '  and  is  essential  to  any  in- 
duction coil. 

+    ,.'P    -    ,'N 


T 


V 


^^ 


Fig.  12. — Diagram  of  the  electrolytic  interrupter.  P,  terminal  of  the  positive 
electrode;  A',  terminal  of  the  negative  electrode;  T,  procelain  sheath  or  tube  cov- 
ering the  positive  electrode;  /,  platinum  point  of  the  positive  electrode;  L,  negative 
electrode   constructed    of   lead. 

There  are  two  classes  of  these  instruments,  both  of 
which  utilize  some  automatic  principle,  and  are  known 
as  "mechanical"  and  "electrolytic." 

Mechanical  interrupters,  a  simple  illustration  of  which 
is  the  ordinary  vibrator  used  on  small  coils,  electric  bells, 
etc.,  will  rapidly  make  or  break  the  primary  current  and 
thereby  induce  a  fairly  constant  current  in  the  secondary ; 
but  this  form  of  interrupter  has  not  been  found  to  be  so 
satisfactory  for  x-ray  work  as  the  electrolytic  type. 


X-RAY    MACHIXES 


CJ 


<r  "th:.  .iiT?''^'''f1  °^  the  induction  coil.  C,  induction  coil;  P,  "the  primary" 
s^'at  InH  fndn^f  ^=  ^'  f'^'^t'-olytic  interrupter  in  circuit  with  the  ^rin^ary  coil;  /"rheo- 
stat and  inductance  control;  X,  x-ray  tube  connected  to  the  terminals  of  the  secondary 


4s  DENTAL   AND    ORAL   RADIOGEAPHY 

Of  the  various  forms  of  electrolytic  interrupters,  the 
Wehnelt  type  is  the  one  most  miiversally  used.  It  con- 
sists of  a  large  battery  jar  which  is  nearly  filled  with  a 
solution  composed  of  sulphuric  acid  one  part  and  water 
six  parts.  Into  this  solution  are  introduced  two  elec- 
trodes. The  negative  electrode  is  constructed  of  lead  and 
has  a  large  surface  exposed,  while  the  positive  electrode 
is  contained  within  a  porcelain  or  hard  rubher  tube  ex- 
tending down  into  the  solution  with  only  the  tip  or  end  of 
the  electrode  exposed.  The  tip  of  this  electrode  is  usually 
made  of  platinum.     (See  Figs.  12  and  13.) 

The  electrolytic  interrupter  is  connected  in  the  primary 
circuit  and  operates  briefly  as  follows:  As  the  current 
passes  from  the  platinum  point  (the  positive  electrode) 
through  the  solution  to  the  negative  electrode,  by  virtue 
of  its  chemical  action  upon  the  solution  bubbles  of  gas 
are  formed  around  the  exposed  platinum  point.  These 
bubbles  act  as  a  source  of  insulation  and  the  current 
ceases  to  flow — "It  is  interrupted."  At  the  instant  it  is 
interrupted,  the  bubbles  are  dispersed,  the  solution  again 
comes  in  contact  with  the  electrode,  and  the  current  is  re- 
established only  to  be  broken  again  and  so  on,  these 
changes  taking  place  with  tremendous  frequency.  With 
such  an  instrument  the  primary  current  may  be  inter- 
rupted from  60  to  30,000  times  a  minute.  These  inter- 
rupters are  sometimes  constructed  with  several  platinum 
points  which  makes  possible  a  greater  amperage  in  the 
current  without  decreasing  the  rate  of  interruptions.  For 
dental  radiography,  however,  a  single  point  interrupter 
will  usually  suffice,  and  at  most,  not  more  than  a  two 
point  interrupter  need  be  used. 

The  interrupter,  then,  serves  the  purpose  of  creating 
the  magnetic  impulses  which  keep  a  constant  current  flow- 
ing from  the  secondary.  We  should  bear  in  mind,  how- 
ever, that  the  current  produced  by  the  "make"  and 


X-RAY    MACHIXES 


49 


"break"  are  not  currents  of  equal  strength,  the  current 
produced  at  tlie  ''break"  liaving  much  the  liig'hest  value. 
The  fact  that  this  current  is  the  strongest,  and  that  the 
magnetic  impulses  come  from  the  same  direction  (as  the 


Fig.    14. — Induction   coil    adapted   for   use   in   the   dental   x-ray    laboratory. 

induction  coil  is  used  on  the  direct  current)  it  prevails 
over  the  weaker.  Therefore  the  induced  or  secondary 
current  which  Ave  use  to  energize  the  x-ray  tube  is  the 
current  which  is  created  at  the  instant  of  the  break. 


50 


DENTAL   Als^D    OEAL    RADIOGRAPHY 


Fig.    15.— Induction    coil    adapted   for    use   in   the    dental   x-ray    laboratory. 


X-RAY    MACHINES 


51 


Fig.    16.-I„ductio„   coil   adapted    for    use    in   the    dental   x-ray   laboratory. 


52  DENTAL   AND    OKAL    RADIOGRAPHY 

The  other  wave,  or  that  created  by  the  "make,"  is 
current  in  the  wrong  direction,  and  is  called  "inverse 
current."  In  some  induction  coils  this  inverse  current 
is  the  source  of  much  trouble,  and  where  it  is  present 
to  any  appreciable  extent,  will  result  in  blurred  radio- 
grams. It  can  be  controlled,  however,  by  the  use  of 
"valve  tubes,"  or  a  "spark  gap,"  arranged  in  series  with 
the  x-ray  tube,  the  valve  tube  or  spark  gap  serving  the 
function  of  cutting  out  the  weaker  or  inverse  current, 
without  interfering  to  any  appreciable  extent  with  the 
stronger  current  which  is  delivered  to  the  terminals  of 
the  x-ray  tube. 

The  induction  coil  is  used  on  the  direct  current  of  110 
or  220  volts.  Where  only  the  alternating  current  is  avail- 
able, some  means  must  be  used  to  change  the  current  from 
alternating  to  direct  before  it  enters  the  primary  circuit 
of  the  coil. 

This  change  in  the  current  can  be  accomplished  by 
the  use  of  "  a  rotary  converter, ' '  of  which  several  makes 
are  available,  or  by  a  "  chemical  rectifier. ' '  These  recti- 
fiers generally  consist  of  two  electrodes  immersed  in  a 
solution  of  the  phosphate  salts  of  potassium,  sodium,  or 
ammonium,  one  electrode  being  made  of  aluminum,  and 
the  other  of  lead„  iron,  or  carbon.  When  working  prop- 
erly, the  current  will  flow  to  the  aluminum  through  the 
solution,  but  not  away  from  it,  thus  cutting  out  one  wave 
of  the  alternating  current;  or  it  is  possible,  by  properly 
connecting  up  three  or  four  jars  containing  the  electrodes, 
to  utilize  both  waves  of  the  current. 

Induction  coils  are  usually  rated  as  to  power  by  the 
maximum  width  of  the  secondary  spark  gap ;  that  is,  the 
amount  of  distance  the  spark  will  jump  between  the  sec- 
ondary terminals.  For  example,  a  12-inch  induction  coil 
is  capable  of  producing  a  spark  that  will  jump  twelve 
inches  of  atmosphere.    While  these  coils  are  made  in  va- 


X-RAY    MACHIlSrES  53 

rious  sizes,  capable  of  producing  a  spark  from  six  inches 
to  forty  inches  in  lengtli,  there  is  no  particular  advantage 
in  using  more  than  a  12-inch  coil  for  dental  radiography. 
(See  Figs.  14,  15,  and  16.) 

Tesla,  or  High  Frequency,  Coil 

The  Tesla,  or  high  frequency,  coil  differs  considerably 
in  construction  from  the  induction  coil,  although  many 
of  its  principles  are  the  same  (Fig.  17).  In  a  way  it  is 
a  double  induction  coil  with  the  secondary  of  one  coil 
acting  as  the  primary  of  the  other  coil.  An  alternating 
current  is  utilized  in  the  i^rimary  of  the  first  coil  and  by 
means  of  the  secondary  of  this  same  coil  is  stepped  up 
to  a  high  voltage.  This  ''stepped-up"  current  is  then 
carried  to  a  condenser.  As  the  current  leaves  the  con- 
denser, it  is  oscillating  at  a  great  rate  of  frequency  and 
passes  into  the  primary  of  the  Tesla,  or  second,  coil 
where  it  induces  a  current  in  the  secondary  of  this  coil. 
From  the  terminals  of  the  last  secondary,  it  is  carried  to 
the  x-ray  tube.  The  principles  involved  in  this  type  of 
apparatus  are  sho^^ai  in  Fig.  17. 

Like  the  current  of  the  induction  coil,  the  current  from 
the  Tesla  coil  is  high  in  voltage  and  low  in  amperage,  but 
unlike  the  current  from  the  induction  coil  it  is  not  uni- 
directional, but  is  alternating  in  character.  For  this  rea- 
son, it  is  considered  by  some  as  being  less  desirable  for 
radiographic  purposes.  However,  this  apparently  ob- 
jectionable feature  is  overcome  by  using  an  x-ray  tube 
constructed  in  such  a  way  as  to  cut  out  one  wave  of  the 
current  and  thereby  produce  practically  the  same  result 
as  where  a  unidirectional  current  is  used. 

These  coils  have  the  advantage  of  being  less  cumber- 
some, require  less  space  and  are  less  expensive  than  the 
other  form  of  apparatus,  but  they  can  not  be  depended 
upon  to  do  the  character  of  work  that  the  powerful  "in- 


54 


DENTAL   AND    ORAL   EADIOGRAPHY 


■O- 


VVW\A 

AAA 


ci 


^ 


VwvwwwwW 

AAAAAAAM 


Fig.  17. — Diagram  of  the  high  frequency  coil.  T,  alternating  current  transformer; 
C,  condenser;  G,  spark  gap;  R,  oscillation  transformer;  D,  high  tension  discharge  gap.; 
X,   high   frequency   5c-ray   tube. 


X-RAY    MACHINES 


55 


duction  coil"  or  "interrupterless  transformer"  will  do. 
Notwithstanding  this  fact,  this  type  of  apparatus  un- 
doubtedly has  a  place  in  the  x-ray  laboratory  of  the  den- 
tist, and  if  constructed  along  proper  lines  can  render 
splendid  service.  Three  sizes  of  these  coils  are  sho^^^l  in 
Figs.  18,  19,  and  20. 


Fig.    18. — Small   type    high   frequency    coil. 


Fig.    19. — Medium-sized    high    frequency   coil. 

Interrupterless  Transformer 

The  interrupterless  transformer  is  the  newest  and  by 
all  means  the  most  powerful  x-ray  machine  made.  Aside 
from  controlling  and  measuring  apparatus,  it  consists 
of  three  principal  parts,  a  rotary  converter,  if  direct  cur- 
rent is  the  source  of  supply,  or  a  synchronous  motor  if 


56 


DENTAL    AND    ORAL   EADIOGRAPHY 


the  alternating  current  is  the  source  of  supply,  a  step-up 
transformer,  and  a  rectifying  smtch. 

Two  types  of  these  machines  are  made;  viz.,  a  direct 


Fig.    20. — Large   type   high   frequency    coil. 


current  machine,  and  an  alternating  current  machine,  the 
underlying  principles  of  which  are  shown  in  Fig.  21.  . 
When  used  on  the  direct  current,  the  rotary  converter 


X-EAY    MACHIlSrES 


57 


is  set  in  motion  and  generates  an  alternating  current 
which  is  sent  through  the  primary  of  the  step-np  trans- 
former. This  induces  a  current  in  the  secondary  of  the 
proper  voltage,  but  alternating  in  character.  The  rectify- 
ing switch  then  changes  this  current  from  an  alternating 


sr^CHffo^Ol/S  mrofi 


t^ 


Fig.  21. — The  working  principles  of  the  interrupterless  transfornTer  are  here 
shown.  The  synchronous  motor  used  to  operate  the  rectifying  switch  of  the  alter- 
nating current  machine  may  also  be  used  as  a  rotary  converter  where  the  direct  cur- 
rent is  desired  for  other  purposes  in   the   laboratory. 

to  a  direct  current  and  as  such  it  is  delivered  to  the  ter- 
minals of  the  tube. 

The  alternating  current  machine  differs  only  from  the 
direct  current  machine  in  that  the  alternating  current  is 
run  directly  into  the  primary  of  the  step-up  transformer. 
This  induces  a  current  in  the  secondary  of  proper  voltage 


05  DENTAL   AND    ORAL    RADIOGRAPHY 

but  alternating  in  character.  The  rectifying  switch  then 
changes  this  high  voltage  alternating  current  to  a  direct 
current,  and  as  such  it  is  carried  to  the  terminals  of  the 
tube. 

The  interrupterless  transformer  is,  as  stated  before, 
the  most  iDowerful  and  efficient  type  of  apparatus  avail- 
able for  x-ray  work.  It  is  likewise  the  most  expensive, — 
too  expensive  in  fact  to  be  considered  for  the  x-ray  lab- 


Fig.   22. — Interrupterless  transformer  adapted   for  use  in  the  dental   x-ray   laboratory. 

oratory  of  the  average  practitioner  of  dentistry,  in  view 
of  the  fact  that  with  the  induction  coil  and  other  less  ex- 
pensive apparatus  such  excellent  results  can  be  obtained. 
The  preceding  remark,  however,  should  not  be  con- 
strued as  an  argument  against  the  interrupterless  trans- 
former. To  the  prospective  purchaser  who  desires  the 
very  best,  regardless  of  expense,  or  who  expects  to  do  a 
great  deal  of  radiography,  the  initial  expense  should  not 


X-RAY    MACHIj^ES 


59 


be  the  prime  consideration,  as  oftentimes  the  most  ex- 
pensive things  in  the  long  run  prove  a  matter  of  economy. 
In  conclusion,  I  would  emphasize  the  fact  that  the  char- 


Fig.   23. — Interrupterlcss   transformer  adapled   for   use   in  the  dental   x-ray   laboratory. 

acter  of  the  radiography  which  any  physician  or  dentist 
is  able  to  do,  does  not  depend  entirely  upon  the  excellence 
of  his  laboratory  equipment.    Instances  could  easily  be 


60 


DENTAL   AND    ORAL   EADIOGRAPHY 


Fig.   24. — Iiiterrupterless   transformer   adapted  for  use  in   tlie   dental  x-ray   laboratory. 


X-RAY    MACHINES  61 

cited  where  the  best  of  equipment  fails  to  produce  the 
highest  type  of  results,  and  vice  versa,  where  unpreten- 
tious equipment  in  some  hands  has  proved  more  than 
satisfactory.  After  all,  the  comparative  degree  of  effi- 
ciency of  the  various  type  of  x-ray  machines  must  depend 
largely  upon  the  judgment  and  skill  of  those  who  operate 
them. 

In  Figs.  22,  23,  and  24  several  interrupterless  trans- 
formers adapted  for  use  in  the  dental  x-ray  laboratory 
are  shown. 


CHAPTER  V 

REQUISITES  OF  THE  DENTAL  X-RAY 
LABORATORY 

The  requisites  of  a  dental  x-ray  laboratory  are  not 
numerous  but  consist  of — 

1st — A  so-called  x-ray  machine. 

2nd — An  x-ray  tube. 

3rd — An  adjustable  "tube  stand"  for  holding  the  tube, 
which  should  include  a  ''tube  shield"  made  of  leaded 
glass,  serving  as  a  means  of  confining  the  rays  and  as  a 
source  of  protection  to  the  operator,  and  a  lead  ''com- 
pression diaphragm"  and  lead-lined  "compression 
c^dinder. ' ' 

4th — A  photographic  darkroom. 

As  x-ray  machines  have  already  been  discussed,  let  us 
now  take  up  the  others,  in  the  order  in  which  they  have 
been  2:iven. 


b' 


X-ray  Tube 

The  x-ray  tube  is  a  thin  glass  bulb  six  or  eight  inches 
in  diameter,  having  two  elongations  or  stems  projecting 
from  the  bulb  opposite  and  in  line  with  each  other  (see 
Fig.  25).  One  of  these  elongations  has  within  it  a  sheet 
iron  tube  at  one  end  of  which  is  a  block  of  copper,  faced 
with  platinum  or  tungsten,  and  set  at  an  angle  of  45  de- 
grees. The  other  end  of  this  sheet  iron  tube  carries  a 
platinum  wire  which  is  sealed  into  the  glass  at  the  end  of 
the  elongation  and  connected  to  a  cap  on  the  outside 
which  serves  as  an  electrical  connection. 

The  other  elongation  carries  a  rod  at  one  end  of  which 
is  a  concave  aluminum  reflector,  the  other  end  being  con- 

62 


KEQUrSITES    OF    DENTAL    X-HAY    LABORATOIIY  ()o 

nected  by  means  of  a  platinum  wire  sealed  in  the  glass  to 
a  cap  on  the  outside  of  the  elongation,  and  also  serves 
as  an  electrical  connection. 

The  cancave  reflector  is  knoAvn  as  ''the  cathode"  and 
the  metallic  block  opposite  it  and  located  upon  the  end 
of  the  sheet  iron  tnbe  is  knoA\ai  as  the  "target"  or 
"anode."  Above  the  anode  and  at  an  angle  there  is  an- 
other stem  projecting  which  carries  a  metallic  terminal 
known  as  the  "assistant  anode." 

This  assistant  anode  has  a  platinum  wire  extending 
from  it  which  is  sealed  into  the  glass  and  connected  to  a 
metallic  cap  on  the  outside  of  the  tube.  The  outer  ter- 
minals of  the  assistant  anode  and  the  anode  are  connected 
by  means  of  a  spiral  spring. 

Directly  above  the  anode  on  the  top  of  the  tube  there 
is  a  small  chamber  with  an  arm  extending  from  it  at  right 
angles.  This  is  known  as  "the  regulating  chamber." 
The  arm  extension  of  this  chamber  is  filled  mth  asbestos 
impregnated  with  chemicals,  and  arranged  about  or  AAith- 
in  a  small  metal  tul)e  from  which  a  platinum  wire  ex- 
tends, is  sealed  into  the  glass  and  connected  to  a  metallic 
cap  on  the  outside  end  of  the  chamber  arm. 

Before  being  finally  sealed,  the  tube  is  pumped  to  a 
high  degree  of  vacuum  (about  1/100,000  part  of  an  atmos- 
phere), only  enough  air  being  left  in  it  to  afford  a  path 
for  the  passage  of  the  electric  current. 

Three  general  types  of  tubes  are  made  for  radiographic 
work,  all  of  which  embody  the  same  general  principles 
but  vary  according  to  the  type  of  the  machine  upon  which 
they  are  to  be  used. 

They  are  designated  as  follows : 

1.  The  coil  tube. 

2.  The  transformer  tube. 

3.  The  high  frequency  tube. 

Coil  tubes  and  transformer  tubes  are  similar  in  con- 


64  DENTAL   AISTD    ORAL   RADIOGRAPHY 

struetion  but  not  in  vacuiim  (see  Fig.  26).  Coil  tubes 
are  exhausted  to  a  much  higher  degree  of  vacuum  in  or- 
der to  lessen  the  tendency  for  inverse  current,  and  give  a 
high  degree  of  penetration.  The  transformer  tube  is 
made  comparatively  low  in  vacuum  as  the  current  from 
the  transformer  is  entirely  free  from  inverse,  and  of  such 
high  voltage  that  the  high  vacuum  is  neither  necessary 
nor  advisable. 

The  high  frequency  tube  differs  slightly  in  construc- 
tion from  the  coil  and  transformer  tubes  owing  to  the 
fact  that  the  high  frequency  current  is  not  unidirectional. 
Therefore,  a  means  must  be  resorted  to  for  cutting  out 
or  disposing  of  one  wave  of  the  alternating  current.  This 
is  accomplished,  as  shown  in  Fig.  27,  by  placing  the  anode 
or  target  in  the  position  occupied  in  the  coil  tube  by  the 
assistant  anode  except  that  it  extends  down  to  the  center 
of  the  tube.  Then  by  having  what  really  amounts  to  two 
cathode  terminals,  only  one  of  which  is  focused  against 
the  face  of  the  anode,  and  the  other  into  a  funnel  in  the 
back  of  the  target,  almost  the  same  effect  is  produced  as 
results  from  a  unidirectional  current. 

Connecting  the  Tube  to  the  X-ray  Machine 

In  connecting  up  the  tube  to  a  coil  or  transformer 
(Fig.  28),  the  anode  terminal  (A)  is  connected  by  means 
of  a  wire  cord  coming  from  a  reel  attached  to  the  posi- 
tive terminal  of  the  machine  {A'),  and  the  cathode  ter- 
minal (C)  is  connected  in  a  similar  manner  to  the  nega- 
tive terminal  of  the  machine  C")- 

A  third  wire  cord  is  usually  run  from  a  reel  {R')  sit- 
uated on  the  coil  near  the  negative  terminal  to  the  cap  on 
the  regulating  chamber  (R).  This  third  terminal  on  the 
coil  has  a  spark  gap  between  it  and  the  negative  terminal 
the  length  of  which  is  adjustable  (designated  by  S'  and 
S). 


KEQUISITES    OF    DENTAL    X-IIAY    LABOEATOKV 


Of) 


Operating  the  X-ray  Tube 

When  the  current  is  started  in  the  machine,  it  enters 
tlie  tube  at  the  anode  and  passes  across  the  gap  to  the 
cathode,  from  which  it  is  reflected  back  as  the  invisible 
cathode  stream  to  strike  a  focal  point  on  the  target  where 
the  x-rays  are  produced  and  pass  out  tlirough  the  walls 
of  the  tube  (see  Fig.  25). 

With  the  passing  of  the  current  througli  the  tube,  it 
should  light  up  in  a  characteristic  manner,  forming  two 
hemispheres  which  have  a  definite  line  of  demarcation. 


A — Anode. 
i-B- -Assislam  Anode 
C— Cathode 
D— Regulating 

Chamber 
F— Regulating      Ad 

juster 
G— Hcinispheie 
H-Conned.on 

Wire 
I— Assistant    Anode 

Cap 
K— Anode   Cap 
L— Cathode    Cap 
M— Cathode  Stream 
N— Focal    Point 


Fig.  25. — Diagram  of  an  x-ray  tube. 

The  hemisphere  in  front  of  the  target  which  is  the  active 
hemisphere,  is  evidenced  by  a  green  fluorescence,  the 
shade  of  coloring  depending  upon  the  degree  of  vacuum 
of  the  tube.  The  fluorescence  of  a  highly  exhausted  tube 
will  be  a  light  yellowish  green,  a  tube  low  in  vacuum  will 
show  a  bluish  green,  while  a  medium  tube  will  be  an  inter- 
mediate green. 

For  dental  radiography,  a  fairly  high  tube  is  indicated 
and  its  vacuum  should  be  kept  as  nearly  uniform  as  pos- 
sible. This  is  made  possible  by  utilizing  the  third  ter- 
minal from  the  x-ray  machine.  By  placing  the  spark  gap 
of  tliis  terminal  about  three  or  four  inches  from  the  nega- 


66 


DEN'TAL   AND    ORAL   RADIOGEAPHY 


tive  terminal  of  the  machine,  the  current  will,  when  the 
vacuum  of  the  tube  gets  high  enough  to  resist  its  pas- 
sage, pass  over  the  gap,  down  the  third  terminal  wire 


Fig.    26. — The   coil   or   transformer   tube. 


into  the  regulating  chamber  where  by  heating  the  as- 
bestos it  will  liberate  gas  and  thereby  reduce  the  vacuum 
of  the  tube. 


REQUISITES    OF    DENTAL    X-IIAY    LABORATORY 


67 


In  addition  to  tlie  general  types  of  tubes  already  de- 
scribed, there  are  certain  specialized  forms  of  tubes  which 


Fig.    27. — The   high  frequency   tube. 


are  highly  useful,  and  fast  becoming  popular.  Of  these, 
the  ''hydrogen  tube"  and  the  ^Coolidge  tube"  are,  by 
far,  the  most  important. 


DENTAL    AND    ORAL    EADIOGRAPHY 


Fig.   28. 


Fig.    29. — The    hydrogen    tube. 


IlIi(iLJlSlTl-:S    OF    DENTAL    X-1L\V    LABOIIATOUY  (J!J 

Hydrogen  Tube 

The  hydrogen  tube,  shown  in  Fig.  29,  differs  from  the 
ordinary  gas  tube  in  that  in  addition  to  having  the  reduc- 
ing feature,  in  common  with  other  tubes,  it  has  the  added 
advantage  of  having  a  raising  device.  This  means  that 
the  hydrogen  tube  may  be  raised  or  lowered,  at  will.  As 
the  name  implies,  this  tube  contains  hydrogen,  Avhich  is 
greatly  responsible  for  its  unusual  flexibility. 

It  is  claimed  for  this  tube  that  it  has  a  slightly  greater 
penetration  than  other  tubes  for  a  given  parallel  spark 


Fig.    30. — The   Coolidge   x-ray   tube. 


length.  The  target  is  made  of  tungsten,  and  the  cathode 
is  protected  in  the  same  manner  as  the  tubes  already 
mentioned. 

Coolidge  Tube 

The  Coolidge  tube,  shown  in  Fig.  30,  is  radically  dif- 
ferent in  design  from  the  other  tubes  already  described, 
and  is  ditferent  in  operation,  in  that  it  is  energized  by 
two  independent  currents,  one  of  high  voltage,  and  the 
other  of  low  voltage.  For  this  reason,  certain  auxiliary 
apparatus  must  be  used  with  it,  in  addition  to  the  x-ray 
generator.  This  auxiliary  apparatus  consists  of  a  low 
voltage  transformer  and  regulator,  and  an  insulated 
stand  or  shelf  for  holding  the  transformer,  and  an  am- 
meter.   The  low  voltage  current  serves  the  purpose  of 


70  DENTAL   AND    OEAL   EADIOGKAPHY 

heating  electrically  a  spiral  filament  of  flat,  closely  wound 
tungsten  wire  located  within  a  cylinder  on  the  cathode. 
This  electrically  heated  filament  serves  the  important 
function  of  controlling  the  milliamperage  of  the  current 
passing  through  the  tube.  The  higher  the  filament  tem- 
perature, the  larger  the  number  of  milliamperes  will  flow 
through  the  tube  and  hence  the  shorter  will  be  the  ex- 
posure required. 

This  tube  is  fast  becoming  popular,  due  to  the  fact  that 
it  is  rugged  of  construction,  will  stand  hard  and  continu- 
ous service,  and  because  of  its  ease  of  control,  will  give 
uniform  results. 

Tube  Stand 

The  tube  stand,  Avhich  serves  the  purpose  of  holding 
the  tube,  should  be  sufficiently  heavy  to  support  it  against 
motion  and  vibration,  and  should  be  sufficiently  adjust- 
able so  that  the  tube  can  be  raised  or  lowered,  or  placed 
at  any  desired  angle.  Its  base  should  be  mounted  upon 
casters  so  that  it  may  be  moved  with  ease.  Such  a  tube 
stand  is  shown  in  Figs.  31  and  32. 

Tube  Shield,  Compression  Diaphragm,  and  Compression 

Cylinder 

The  tube,  tube  stand,  tube  shield,  compression  dia- 
phragm and  compression  cylinder,  when  adjusted  for 
work,  as  shown  in  Figs.  31  and  32,  really  comprise  a 
single  piece  of  apparatus.  Bearing  in  mind  the  fact  that 
the  x-rays  pass  out  in  every  direction  from  the  face  of 
the  anode,  or  target,  (see  Fig.  33-^)  which  is  situated  in 
the  center  of  the  tube,  it  is  necessary,  if  the  clearest  pos- 
sible shadows  are  to  be  produced,  to  use  only  those  rays 
that  have  the  same  general  direction  and  that  have  an 
equal  amount  of  penetration.  Now  it  is  known  that  the 
most  rapid  and  effective  rays  are  those  that  pass  out  at 


REQUISITES    OF    DENTAL   X-RAY   LABORATORY  71 


Fig.  31. — The  tube  stand. 


72 


DENTAL    AND    ORAL   RADIOGEAPHY 


Fig.   32.— Illustrating   how   tlie   tube   may  be   placed   at   any    desired   angle. 


REQUISITES    OF    DENTAL    X-1!AY    i.AllOKATOItV 


(6 


Fig.   33-A. 


Fig.   33-C. 


74 


DENTAL   AND    OKAL   KADIOGRAPHY 


right  angles  from  the  cathode  stream  designated  by  PR. 
Inasmuch  as  we  desire  to  nse  these  rays,  and  these  rays 
only,  in  casting  our  shadows,  we  must  establish  some 
means  of  preventing  the  other  rays  {S,S,S,S)  from  es- 
caping from  the  immediate  area  surrounding  the  tube, 
and  this  is  accomplished  by  means  of  the  tube  shield, 
compression  diaphragm,  and  compression  cylinder. 

The  tube  shield  (Fig.  34),  a  sectional  diagram  of  which 
is  shoA^m  in  Fig.  33-Z?  by  TS  is  made  of  leaded  glass, 
there  being  a  sufficient  amount  of  lead  in  the  glass  to 


Fig.   34. — Leaded  glass  tube  shield. 

prevent  ordinary  rays  from  passing  through  it.  The 
compression  diaphragm  makes  up  the  floor  of  the  tube 
shield  (D),  and  is  constructed  of  sheet  lead  with  an  open- 
ing of  the  proper  size  to  allow  the  desired  rays  to  pass 
through.  The  compression  c^dinder  (CC)  (Fig.  33-C)  is 
made  of  aluminum  with  a  lead  lining  that  absorbs  any 
secondary  rays  that  have  succeeded  in  passing  through 
the  diaphragm.  It  should  be  apparent  to  anyone  that 
with  this  apparatus,  the  only  x-rays  that  succeed  in  leav- 
ing the  immediate  area  of  the  tube  are  those  that  are 
used  to  cast  the  shadows  of  the  parts  desired,  which  is 


EEQUISITES    OF    DENTAL    X-KAY   LABORATORY 


75 


of  great  importaneo,  not  only  in  obtaining  radiograms 
that  are  sharp  and  clear  and  uniform,  hut  also  to  the 
health  of  the  operator  and  others  associated  with  him  in 
the  office. 

Arrangement  of  the  Apparatus  in  the  Office 

If  dental  x-ray  equipment  is  desired,  the  question  nat- 
urally arises,  "Where  can  the  necessary  apparatus  be 


Fig.   35. — A  convenient  manner  of  arranging  the  necessary  apparatus  when  not  in  use. 

placed?"  While  a  separate  room  is  desirable,  it  is  by 
no  means  necessary,  as  the  ordinary  operating  room  of 
"healthy  size"  can  be  made  to  accommodate  it. 

The  coil  or  transformer,  and  the  tube  stand  can  be 
placed  against  the  v/all  at  the  left  of  the  room,  while  the 
tubes  can  be  hung  in  a  suitable  rack  upon  the  wall  where 
they  will  be  out  of  harm's  way  (Fig.  35).  Arranged  in 
this  manner,  x-ray  apparatus  is  not  in  the  way,  and  is 
accessible  for  use  at  any  time. 


76  DENTAL   AND    ORAL   EADIOGRAPHY 

The  dental  chair  with  its  multitude  of  adjustments 
serves  an  important  purpose  in  the  dental  x-ray  labora- 
tory, for  the  patient  must  be  supported  in  such  a  manner 
as  to  be  able  to  hold  perfectly  quiet  during  the  time  the 
exposures  are  made.  Owing  to  the  stability  of  the  chair 
and  its  many  adjustments,  it  mil  not  only  serve  this  pur- 
pose, but  is  preferable  to  having  the  patient  lie  upon  a 
table  which  has  been  the  method  employed  by  many  radi- 
ographers in  the  past. 

Photographic  Darkroom 

Thus  far  we  have  discussed  all  but  one  of  the  requisites 
of  the  dental  x-ray  laboratory;  viz.,  the  photographic 
darkroom.  This  is  a  very  important  requisite,  and  any- 
one attempting  to  do  radiography  without  it  is  greatly 
handicapped.  It  need  not  be  large  or  elaborate,  and  run- 
ning water  is  not  absolutely  essential,  although  it  is  an 
advantage.  A  closet  3^x5  feet  will  suffice  if  nothing  bet- 
ter is  available.  A  broad  shelf  should  be  placed  at  one 
end  to  hold  the  developing  trays  and  other  photographic 
accessories. 

With  a  darkroom  always  available,  the  dental  radiog- 
rapher is  able  to  develop  his  plates  or  films  immediately, 
profit  by  their  findings,  or,  in  case  they  do  not  come  out 
satisfactorily,  make  others  without  subjecting  the  patient 
to  the  inconvenience  of  another  appointment. 

Where  limited  space  precludes  the  possibility  of  a  reg- 
ular darkroom,  a  developing  cabinet,  or  so-called  "port- 
able darkroom"  may  be  utilized.  (See  Fig.  36.)  Such 
a  cabinet  may  be  placed  upon  a  small  table  or  attached  to 
the  wall  at  the  proper  height  from  the  floor.  It  should  be 
large  enough  to  contain  the  necessary  developing  trays 
and  other  photographic  necessities.  The  front  panel 
should  be  hinged  so  as  to  permit  easy  access  to  the  in- 
terior for  the  arrangement  of  the  trays,  solutions  and 


REQUISITES    OF    DENTAL    X-IIAY    LABOItATORY 


it 


for  their  removal  after  development.  The  riihy  lamp  for 
lighting  the  interior  slionld  l)e  an  integi-al  part  of  tlie 
cabinet  and  the  "observation  windoAv"  at  the  top  shonld 
be  so  placed  that  the  operator  can  have  an  nnobstructed 
view  of  the  interior.  This  window  must  be  covered  with 
ruby  glass,  and  around  it  should  be  constructed  a  shield 


Fig.    36. — The    portable   darkroom. 

which  will  shut  out  all  outside  light  while  the  operator 
is  looking  into  the  cabinet. 

,  With  the  portable  darkroom,  plates  and  films  may  be 
satisfactorily  developed,  but  the  process  can  not  be  car- 
ried with  the  same  degree  of  comfort  as  where  "a  reg- 
ular darkroom"  is  available.  Therefore,  any  dentist  in- 
tending to  do  any  considerable  amount  of  radiography 
can  well  afford  to  go  to  the  trouble  and  expense  of  con- 
structing a  darkroom  which  will  be  comfortable,  and  con- 
lain  all  the  conveniences. 


CHAPTER  VI 
TECHNIC  OF  DENTAL  AND  ORAL  RADIOGRAPHY 

Having  discussed  the  requisites  of  the  dental  x-ray 
laboratory,  let  us  now  proceed  to  a  consideration  of  their 
application  in  the  actual  work  of  radiography. 

The  very  nature  of  the  structures  with  which  Ave  con- 
cern ourselves,  their  gross  as  well  as  minute  anatomy, 
renders  them  somewhat  difficult  to  radiograph,  and  neces- 
sitates a  refinement  of  technic  greater  than  that  de- 
manded for  most  of  the  other  portions  of  the  human  an- 
atomy. It  would,  therefore,  seem  obvious  that  an  ac- 
curate knowledge  and  anatomic  appreciation  of  the 
structures  of  the  oral  cavity  and  associated  organs  and 
structures  is  the  first  requisite  for  successful  dental  and 
oral  radiography. 

We  should  keep  in  mind  the  fact  that  radiograms  are 
shadow  pictures,  and  that  the  effect  produced  by  the  x- 
ray  upon  the  photographic  plate  is  but  a  shadowgraphic 
representation  of  the  tissues  through  which  the  rays  have 
passed.  We  know  that  this  ray  penetrates  all  matter  in 
inverse  ratio  to  its  mass  or  density,  and  therefore  the 
shadow  picture  which  is  left  upon  the  photographic  plate 
is  simply  a  record  of  the  varying  density  of  the  tissues 
through  which  the  rays  have  penetrated. 

The  x-rays  are  particularly  applicable  to  the  dental  and 
oral  structures,  owing  to  the  fact  that  these  structures 
differ  enough  individually  in  degree  of  density  to  permit 
of  their  appearing  in  a  characteristic  manner  upon  the 
photographic  plate.  For  instance,  it  will  be  noted  upon 
the  examination  of  a  dental  radiogram,  that  metallic  fill- 
ings appear  as  white  masses,  and  root  fillings  as  some- 

78 


DENTAL    AND    ORAL   RADIOGRAPHY    TECIINIC  79 

what  less  dense  lines.  The  enamel  and  dentin  are  next 
in  density,  and  root  canals  show  plainly  as  dark  channels 
in  the  dentin,  while  the  alveolar  process  and  maxillae  show 
their  fine  uniform  cancellous  structure  in  various  degrees 
of  density  depending  upon  their  thickness. 

As  a  tooth  is  much  more  dense  than  the  bony  structures 
of  the  jaw,  any  anomaly  of  form,  size  or  position  in  the 
jaws  is  easily  discernible  even  though  it  occupy  a  posi- 
tion far  from  what  might  be  expected;  as  for  instance, 
impacted  molars,  teeth  in  the  antrum,  etc. 

Due  to  the  fact  that  the  structures  within  the  field  of 
our  specialty  have  a  characteristic  appearance  under  nor- 
mal conditions,  any  alterations  or  change  in  these  struc- 
tures is  at  once  evident  upon  the  plate.  We  thus  are  af- 
forded a  means  of  studying  intra  vitam  the  gross  pa- 
thology of  the  structures  of  the  oral  cavity. 

I  would  again  emphasize  a  point  pre^dously  made ;  viz., 
that  a  radiogram  is  not  a  x)hotograph,  but  a  shadow  pic- 
ture which  is  produced  by  using  the  x-ray  as  the  source 
of  illumination  and  the  photographic  plate  as  a  screen 
for  recording  permanently  the  shadows  cast. 

Therefore,  in  maldng  radiograms,  we  must  adhere  to 
the  same  rules  which  apply  in  making  correct  shadows 
with  ordinary  light.  If  correct  shadows  are  cast,  a  cer- 
tain definite  relationship  must  exist  between  the  source 
of  illumination,  the  object,  and  the  screen.  Any  change 
or  variance  in  this  relationship  will  result  in  a  changed 
image.  A  simple  experiment  will  suffice  to  illustrate  to 
a  beginner  the  truth  of  this  statement. 

Use  a  piece  of  ordinary  white  writing  paper  as  a  screen 
and  hold  it  about  two  feet  away  from  a  lamp,  and  place 
your  hand  or  any  other  small  object,  midway  between  the 
lamp  and  the  improvised  screen,  and  observe  the  shadow 
cast.  You  will  note,  first,  that  it  is  very  much  enlarged ; 
and,  second,  that  it  is  very  faint  and  indistinct.    Now, 


80  DENTAL   AND    OEAL    RADIOGRAPHY 

slowly  move  the  object  toward  the  screen.  As  it  ap- 
proaches, the  shadow  becomes  more  distinct  and  smaller 
mitil  at  length  when  the  object  is  'almost  touching  the 
screen,  the  shadow  will  be  good,  black  and  distinct,  and 
of  practically  the  exact  size  of  the  actual  object.  It  will 
also  be  found  that  the  shadow  can  be  altered  by  chang- 
ing the  position  of  the  light,  that  is,  moving  it  toward  the 
object  or  away  from  it,  by  lowering  it  below  the  level  of 
the  object  or  raising  it  higher  than  the  object ;  or  by  mov- 
ing it  to  the  right  or  to  the  left.  Eventually,  however, 
a  point  can  be  found  which  will  cause  the  shadow  to  as- 
sume its  most  correct  proportions  as  well  as  its  sharp- 
est outline.  When  this  point  is  established,  the  light  rays 
will  be  traveling  in  a  perpendicular  direction  to  a  plane 
which  lies  midway  between  the  plane  of  the  object  and 
the  plane  of  the  screen,  and  the  light  will  be  placed  at 
w^hat  we  call  the  proper  focal  distance. 

Applying  the  laws  deduced  from  this  simple  illustra- 
tion of  shadow  making  to  radiography,  we  learn,  first, 
that  the  closer  we  can  bring  the  photographic  plate  to 
the  tissues  we  wish  to  show,  the  clearer  and  sharper  will 
be  the  resulting  radiogram;  second,  that  the  x-rays  in 
passing  through  the  tissues,  must  travel  perpendicularly 
to  a  line  which  lies  midway  between  the  plane  of  the  tis- 
sues desired  and  the  XDlane  occupied  by  the  photographic 
plate;  and  third,  that  the  source  of  the  x-ray  production 
(the  target  of  the  tube)  must  be  placed  at  a  proper  focal 
distance. 

In  order  to  obtain  a  radiogram  of  any  portion  of  the 
body,  it  is  necessary  to  have  a  photographic  or  x-ray 
plate,  or  film  (properly  prepared  so  as  to  exclude  all  light 
and  moisture),  placed  in  such  a  position  that  the  rays 
passing  through  the  structures  desired,  will  register  their 
shadows  with  the  least  amount  of  distortion  possible  upon 
the  plate. 


DEIN'TAL    AND    ORAL   EADIOGRAPHY    TECHXIC  81 

In  securing  shadowgrapliie  ropTosontations  of  the  den- 
tal and  oral  strnctnres,  two  general  nietliods  of  procedure 
are  open  to  us,  each  of  which  has  its  values  and  special 
indications.  These  are  known  as  the  "inta-oral"  and 
"extra-oral"  methods. 

With  the  first,  only  small  films  are  used  which  are 
placed  within  the  month  opposite  the  area  to  be  radio- 
graphed, and  held  in  position  either  by  means  of  a  tray 
or  film  holder,  or  by  the  assistant,  or  better  still,  by  the 
patient  exerting  slight  pressure  with  the  finger.  This 
method  is  indicated  where  radiograms  of  small  areas  only 
are  desired,  as,  for  instance,  two  or  three  of  the  teeth, 
with  the  adjacent  alveolar  process. 

With  the  other  method  of  procedure  mentioned;  viz., 
the  "extra-oral"  method,  large  plates  or  films  are  used 
and  the  areas  desired  are  brought  in  as  close  contact  as 
possible  with  the  plate  by  pressing  or  resting  the  face 
against  it.  The  x-rays  are  then  passed  through  the  struc- 
tures from  the  other  side  of  the  skull,  and  oftentimes 
must  pass  through  the  entire  face  or  skull,  in  transit. 

When  using  this  method,  large  areas  may  be  radio- 
graphed, which  in  some  instances  will  embrace  the  lateral 
lialves  of  both  the  upper  and  lower  jaws  from  the  cusx)id 
region  anteriorly  to  the  angle  of  the  jaw  posteriorly,  and 
from  the  floor  of  the  orbit  above  to  the  inferior  margin 
of  the  mandible  below.  In  fact,  it  is  possible  by  making 
several  exposures  to  obtain  in  detail  a  shadowgraphic 
representation  of  the  dental  apparatus  in  toto,  as  well 
as  its  associated  organs  and  structures,  the  nasal  cavity 
and  pneumatic  sinuses,  the  maxilla  and  the  mandible. 

It  should  be  apparent  to  anyone  that  the  first  method 
greatly  reduces  the  possibilities  of  the  x-ray.  Both  meth- 
ods have  their  advantages  and  neither  should  be  dis- 
carded in  favor  of  the  other. 


82  DENTAL   AND    ORAL    RADIOGRAPHY 

Intra-oral  Method 

"We  shall  first  discnss  the  intra-oral  method  by  which 
small  areas  are  radiographed.  First  of  all,  the  patient 
should  be  placed  in  a  comfortable  position,  and  the  head 
supported  so  that  it  may  he  held  perfectly  still.  After 
the  tube  has  been  tested  out  and  the  proper  degree  of 
vacuum  established,  the  tube  stand  (complete  with  the 


Fig.  37. — The  patient  can  hold  the  film  in  position  against  the  upper  teeth  by  exerting 
slight   pressure    with   the   thumb. 

other  apparatus  before  described)  is  moved  to  a  position 
where  the  rays  coming  from  the  tube,  through  the  com- 
pression diaphragm  and  cylinder  can  be  made  to  pass 
through  the  desired  areas  and  cast  their  shadows  upon 
the  small  film  within  the  mouth  (Fig.  37). 

In  using  this  method  upon  the  upper  teeth,  the  great- 
est care  must  be  exercised  if  the  shadows  produced  are 
free  from  distortion,  for  the  film  must  be  held  within  the 
upper  arch  against  the  lingual  side  of  the  teeth  and  the 
palate,  and  must  occupy  a  position  which  is  in  a  different 


DENTAL    AND    ORAL   RADIOGRAPHY    TECHNIC 


plane  from  that  occupied  by  the  roots  of  the  teeth.  When- 
ever it  is  necessary  to  direct  the  raj's  upon  structures  tliat 
lie  at  an  angle  with  the  plate  or  film,  correct  shadows 
may  be  obtained  by  adhering  to  the  following  rule :     "Bi- 


Fig.   38. — Correct  and  incorrect  technic. 


sect  the  angle  made  by  the  plane  of  the  object,  and  the 
plane  of  the  film,  and  direct  the  rays  so  that  they  ivill 
fall  perpendicidar  to  this  bisected  plane." 

Failure  to  adhere  strictly  to  this  rule  is  one  of  the 


84  DENTAL    AND    ORAL    RADIOGRAPHY 

most  common  causes  of  partial  or  comxDlete  failure  in 
producing  true  shadowgraphic  representations  of  the 
dental  structures.  For  instance,  if  the  rays  are  directed 
from  too  low  a  source,  the  shadows  will  be  lengthened, 
or  if  they  be  directed  from  too  high  a  source,  the  shad- 
ows will  be  foreshortened,  the  amount  of  elongation  or 
foreshortening  being  in  direct  proportion  to  the  amount 
of  deviation  from  the  proper  focal  point. 

The  importance  of  adhering  strictly  to  this  rule  is 
graphically  shown  in  Fig.  38,*  where  an  upper  central 
incisor  and  the  adjacent  teeth  are  radiographed.  In  the 
upper  picture  {A)  the  rays  are  passing  in  from  too  low 
a  source  with  the  result  that  the  image  imposed  upon  the 
film  is  lengthened  to  the  extent  that  the  resulting  radio- 
gram is  useless.  In  the  center  picture  (B)  the  rays  are 
coming  from  too  high  a  source,  the  result  being  a  short- 
ened image.  Such  a  radiogram  has  but  little  value  and 
in  many  instances  Avould  prove  very  misleading.  In  the 
lower  picture  (C)  the  rays  are  passing  in  at  the  cor- 
rect angle;  viz.,  they  are  directed  perpendicularly  to  a 
plane  which  lies  midway  between  the  plane  of  the  teeth 
desired  and  the  plane  of  the  film.  The  result  is  a  radio- 
gram in  which  the  images  of  the  teeth  desired  are  im- 
posed upon  the  film  in  their  correct  proportions. 

It  will  be  noted  upon  a  close  examination  of  this  last 
radiogram  (C)  that  an  abscess  is  present  upon  the  root 
of  the  right  central  incisor.  By  examining  the  other 
radiograms  {A  and  B)  it  will  be  seen  that  this  condition 
is  not  apparent  in  them,  which  lends  emphasis  to  the 
importance  of  an  exact  technic. 

The  technic  illustrated  (by  C  of  Fig.  38)  is  indicated 
for  all  of  the  upper  teeth.  Occasions  may  arise,  however, 
where  it  will  not  suffice  for  the  upper  molar  teeth  owing 
to  the  fact  that  the  buccal  roots  and  the  lingual  roots  may 


*Technic  of  Dr    Weston  Price, 


])ENTAL    AND    OJIAI.    JtADJOGKAL'Jl  Y    TECJIXIC 


s.-) 


diverge  to  the  extent  of  assuming  different  planes.  In 
this  event,  it  may  be  necessary  to  make  more  than  one 
radiogram,  if  information  of  an  exacting  character  is  de- 


Fig.    39. — Technic   for   the   upper  molar  teeth. 

sired  concerning  an  upper  molar.    The  plan  of  procedure 
is  shown  in  Fig.  39,  A,  B,  and  C. 
If  a  general  picture  of  the  molar  is  desired  (shown  by 


8b  DENTAL   AND    ORAL   RADIOGRAPHY 

A),  the  plane  of  the  tooth  is  assumed  as  lying  midway 
between  buccal  roots  and  lingual  root,  and  the  rays  are 
passed  in  perpendicularly  to  the  plane  lying  midway  be- 
tween this  assumed  plane  and  the  film.  In  the  resulting 
radiogram  none  of  the  roots  will  appear  in  their  exact 
proportions,  but  the  buccal  roots  will  be  slightly  short- 
ened, while  the  lingual  root  will  be  slightly  lengthened. 

When  it  is  desirable  to  obtain  a  radiogram  of  the  buc- 
cal roots  in  their  exact  length,  they  must  be  assumed  as 
being  the  plane  of  the  tooth  (B)  and  the  rays  must  pass 
in  perpendicularly  to  a  plane  lying  midway  between  them 


Fig.    40. — Special    compression   cylinder   made    of   leaded   glass. 

and  the  film.  In  this  event,  the  image  of  the  lingual  root 
is  elongated. 

If  the  lingual  roots  are  under  scrutiny  (C),  they  must 
be  considered  the  plane  of  the  teeth,  and  the  rays  passed 
in  perpendicularly  to  a  plane  lying  midway  between  the 
lingual  root  and  the  film.  In  this  event,  the  image  of 
the  lingual  root  will  have  its  correct  proportions,  but  the 
image  of  the  buccal  roots  will  be  slightly  shortened. 

The  upper  molars  are  by  all  means  the  most  difficult 
teeth  to  radiograph;  that  is,  to  obtain  radiograms  that 
are  as  comprehensive  as  those  made  of  the  other  teeth. 


DENTAL   AND    ORAL   RADIOGRAPHY    TECHNIC  87 

However,  by  going  to  the  extra  work  entailed  by  the 
foregoing  procedure,  valuable  radiographic  information 
can  oftentimes  be  gained. 

The  task  of  radiographing  the  upper  molars  and  pre- 
molars can  be  rendered  less  difficult  by  using  a  special 
compression  cylinder  made  of  leaded  glass,  as  sho^\ni  in 
Fig.  40.*  The  end  of  the  glass  cone  or  cylinder  is  beveled 
at  the  end  so  that  it  can  be  placed  close  to  the  face  and 
still  remain  at  the  desired  angle,  its  glass  construction 


Fig.   41. — The   patient  can   hold  the  film  in  position  against  the   lower   teeth   by   exert- 
ing slight  pressure  with  the   finger. 

enabling  the  operator  to  view  the  area  under  exposure 
at  all  times,  and  thereby  lessen  the  liability  of  inaccurate 
work. 

With  the  lower  teeth  (Fig.  41)  we  do  not  have  this  diffi- 
culty to  contend  with  to  so  great  a  degree,  as  the  films 
can  be  placed  for  the  most  part  in  such  a  position  that 
they  lie  parallel  to  the  long  axis  of  the  teeth,  and  the  rays 
can  be  directed  in  a  perpendicular  direction  both  to  the 
plane  of  the  teeth  and  the  plane  of  the  film. 

In  placing  the  films  in  the  mouth  preparatory  to  mak- 

*  Suggested  by  Dr.  F.  K.  Ream. 


88  dejsttal  a:n^d  oral  eadiogeaphy 

ing  radiograms  of  the  lower  teeth,  difficulty  is  sometimes 
encomitered,  owing  to  the  fact  that  the  tissues  are  usually 
quite  sensitive.  Inasmuch  as  the  film  must  he  pressed 
well  cloivn  between  the  tongue  and  the  teeth,  it  is  advis- 
able to  first  see  that  no  sharp  corners  exist  on  the  film 
covering,  or  better  still,  provide  a  rubber  envelope  or 
film  holder  ivhich  has  no  sharp  corners.  Such  an  en- 
velope is  easih^  improvised  by  the  use  of  ordinary  black 
vulcanite  rubber.  A  loieceof  this  rubber  which  should  be 
a  little  more  than  double  the  size  of  the  film,  is  wrapped 
about  it  and  the  free  edges  pressed  together.  These  edges 
are  then  trimmed  with  a  pair  of  scissors  so  that  the  cor- 
ners are  rounded.  Such  an  envelope  containing  the  film 
can  be  introduced  into  the  mouth  and  placed  well  dovm 
on  the  lingual  side  of  the  teeth  Avitli  a  minimum  amount 
of  discomfort  to  the  patient. 

Film  Holders. — Some  operators  prefer  to  use  a  film 
holder  to  support  the  film  during  exposure.  Of  these, 
there  are  several  varieties  upon  the  market,  all  of  which 
will  accomplish  the  work  for  which  they  are  intended. 

The  Ketcham  Film  Holder.* — The  Ketcham  film 
holder  consists  of  a  metal  block  with  a  rubber  band 
around  it,  Avhich  can  be  cjuickly  changed,  a  bolt  secured 
by  a  wing  nut  to  pass  through  a  slot  in  the  block,  and  five 
]3airs  of  film  holders.  These  film  holders  are  rights  and 
lefts,  and  graded  in  size,  and  shape,  so  as  to  fit  different 
mouths.  (See  Figs.  4:2-A,  B,  and  C.)  A  "stereoscopic 
finder"  is  also  a  part  of  this  set,  which  allows  the  oper- 
ator to  make  a  second  radiogram  of  a  given  area,  by  re- 
moving the  exi^osed  film  and  placing  another  in  its  place 
in  exactly  the  same  ijosition. 

The  Leach  Film  Holder.! — The  Leach  film  holder  is 
very  sim]Dle  in  design,  and  two  film  holders  constitute  a 
set.     (See  Fig.  43.) 

*Des!gned  by  Dr.   A.   H.   Ketcham. 
tDesigned  b}'  Dr.   F.   D.   Leach. 


DENTAL    AND    ORAL   RADIOGRAPHY    TECIINIC 


89 


B. 


C. 


Fig.  42. — The  Kctcham  film  holder.  A,  right  and  left  film  holders  in  graded  sizes; 
B,  metal  block  with  film  holder  attached  to  it  and  film  in  position  ready  to  be  placed 
in  the  mouth.  By  closing  the  teeth  upon  the  metal  block,  the  film  holder  is  held  in 
the  position   desired;    C,   stereoscopic   finder  attached   to   the   film   holder. 


90 


DENTAL   AND    ORAL   EADIOGRAPHY 


With  these,  the  patient  holds  the  film  in  position  by 
grasping  the  handle  part  of  the  holder,  and  the  operator 
can  by  noting  the  angle  of  the  handle,  determine  the  di- 
rection in  which  the  rays  mnst  be  directed. 

The  smaller  holder  is  designed  for  the  upper  six  and 
lower  eight  anterior  teeth,  and  the  larger  holder  is  de- 
signed for  the  posterior  areas  of  the  month. 

The  Dorr  Film  Holder.* — The  Dorr  film  holder  is  de- 
signed so  that  the  film  is  lield  in  position  for  exposure 


Fig.   43.— The  Leach  film  holder. 

by  closing  the  teeth  upon  a  flange  which  is  part  of  the 
holder.  (See  Fig.  44.)  A  removable  handle  is  attached 
to  the  edge  of  the  flange  and  assists  in  placing  the  film 
holder  (carrying  the  film)  in  the  desired  position  in  the 
mouth,  after  which  the  handle  can  be  removed. 

Two  film  holders  constitute  a  set  of  which  one  has  an 
obtuse  angle  and  is  designed  for  the  upper  teeth,  while 
the  other  is  placed  at  right  angles  to  the  flange  and  is 
intended  for  use  upon  the  lower  teeth. 


*Designed  by  Dr.   P.   P.   Dorr. 


DENTAL   AND    ORAL   RADIOGllAPIIY    TECIINIC 


91 


Where  it  is  necessary  to  make  a  complete  radiographic 
examination  of  the  dental  arches,  it  can  be  accomplished 
in  the  average  case,  by  making  six  exposures  of  each 
arch.  The  procedure  to  be  followed  is  diagrammatically 
shoA\ai  in  Fig.  45.  The  numbers  1,  2,  3,  4,  5,  6  indicate  the 
position  of  the  x-ray  tube  in  its  relation  to  the  dental 


Fig.    44. — The    Dorr    film    holder   with    detachable   handle. 


Fig.  45. 

arch,  and  the  ends  of  the  lines  coming  from  the  numbers 
show  the  position  of  the  mesial  and  distal  edges  of  the 
film  used  for  each  exposure.  It  mil  be  noted  that  each 
adjacent  film  position  overlaps  its  neighbor  which  is  ad- 
visable so  that  no  area  is  left  out. 

In  making  radiograms  of  the  anterior  part  of  the  arch, 
it  is  a  mistake  to  attempt  to  radiograph  more  than  two 


92  DENTAL    AND    ORAL   EADIOGRAPHY 

or  three  teeth  at  a  tmie,  as  the  curvature  of  the  arch 
usually  renders  it  impossible  to  get  more  than  that  num- 
ber free  from  distortion. 

Another  point  in  technic  which  should  not  be  over- 
looked if  sharp  outlines  are  to  be  obtained,  is  the  one  in 
regard  to  having  the  tube  placed  at  the  proper  distance 
from  the  structures  to  be  radiogaphed.  To  establish  the 
best  focal  distance  for  work  about  the  teeth  or  jaws,  the 
target  of  the  tube  should  be  about  twenty  inches  from  the 
plate  or  film. 

With  a  good  x-ray  machine,  and  a  properly  regulated 
tube,  good  radiograms  can  be  obtained  by  very  short  ex- 
posures, particularly  by  using  the  intra-oral  method,  as 
the  rays  need  only  penetrate  a  comparatively  short  dis- 
tance before  reaching  the  film.  With  the  apparatus  now 
available  good  radiograms  can  often  be  obtained  by  in- 
stantaneous exposures.  However,  instantaneous  expo- 
sures are  not  necessary  for  good  dental  radiography.  X- 
ray  apparatus  which  is  capable  of  producing  sharp, 
clear  "intra-oral"  radiograms  in  from  two  to  five  sec- 
onds, is  efficient  enough  for  use  in  the  x-ray  laboratory 
of  the  dentist. 

Extra-oral  Method 

The  extra-oral  method  is,  in  the  author's  opinion,  the 
one  offering  the  widest  range  of  usefulness  in  our  work. 
As  stated  previously,  this  is  the  method  used  to  obtain 
radiograms  of  large  areas.  Not  only  can  larger  areas  be 
obtained  by  this  method,  but  locations  and  structures  in- 
accessible to  the  small  films  are  reached  and  their  images 
accurately  and  clearly  recorded  upon  the  larger  plates. 
Therefore,  the  advantage  of  this  method  is  well  founded. 

The  technic  is  simple  when  once  mastered,  but  must  be 
adhered  to  accurately  if  the  results  are  to  be  depended 
upon  for  diagnosis.    In  using  the  extra-oral  method,  large 


DENTAL    AND    OltAL    llADIOGRAPIIY    TECHNIG  93 

plates  or  films  are  used  and  the  areas  desired  are  brought 
in  as  close  contact  as  possible  with  the  plate,  hy  pressing 
or  resting  the  side  or  portion  of  the  face  upon  tvhich 
the  structures  desired  are  located,  against  the  plate. 

First  of  all,  the  patient  must  be  placed  in  a  position  so 
that  the  head  can  he  held  perfectly  still.  The  dental  chair 
with  a  few  adjustments  offers  an  excellent  means  for 
accomplishing  this.  One  of  the  chair  arms  is  lowered 
down  against  the  side  of  the  chair  or  removed,  and  the 


Fig.    46. — The   headrest   of  the   dental   chair   with   its    many    adjustments    can    easily    be 
arranged  so  that  the  patient's   head  may   rest  easily  and   firmly  upon  it. 

patient  placed  sideways  in  the  chair.  The  chair  back  is 
adjusted  so  that  the  patient  lies  against  it  in  an  easy 
position,  and  the  headrest  wings  are  adjusted  so  as  to 
lie  flat  and  thereby  form  an  excellent  resting  x)lace  for  the 
plate.  The  headrest  with  its  many  possible  adjustments 
can  easily  be  placed  so  that  the  patient's  head  rests  easily 
and  firmly  upon  the  plate,  rendering  it  an  easy  matter  to 
remain  perfectly  quiet.  This  position  is  shown  in  Fig. 
46. 


94 


DENTAL   AND    OKAL   EADIOGRAPHY 


Fig.   Al-A. — Tube  stand  with  platerest  and   head  support.      (Eisen  and  Ivy.) 


Fig.  47-B. — Position  of  head  and  angle  for  left  side  of  jaws.      (Eisen  and  Ivy.) 


DENTAL    AND    ORAL   IIADIOGRAPIIY   TECHNIC  95 


Fig.   48. — The   arrangement  of  the  apparatus  preparatory  to   seating  the  patient. 


Fig.  49. — The  patient  seated  and  the  apparatus  arranged  for  making  a  radiogram 
of  the  left  side.  The  comfortable  position  of  the  patient  renders  it  an  easy  matter 
to   remain   perfectly   quiet. 


96  DENTAL    AND    ORAL    RADIOGRAPHY 

For  this  character  of  work  some  operators  prefer  to 
use  a  platerest  and  head  supporting  device  attached  to 
the  tube  stand  as  shoA^ni  in  Fig.  4:7 -A.  Where  such  a 
method  is  followed,  the  head  is  supported  in  its  proper 
relationship  to  the  plate  as  shown  in  Fig.  47-5.* 

Author's  Method  of  Seating  the  Patient 

In  the  author's  opinion,  there  is  another  method  of 
seating  the  patient  for  this  character  of  work  which 
will  be  found  to  be  advantageous  where  such  special  ap- 
paratus is  not  available.  It  is  accomplished  by  using  an 
ordinary  chair  Avith  a  straight  back  and  small  arms, 
placed  against  the  back  of  the  dental  chair.  The  head- 
rest of  the  chair  is  turned  over  and  adjusted  to  the 
proper  height,  position  and  angle,  so  that  the  patient's 
head  can  rest  against  it  in  any  desired  position.  In  this 
way  the  patient  is  afforded  the  firm  support  of  the  heavy 
dental  chair,  and,  therefore,  has  little  difficulty  in  re- 
maining perfectly  quiet,  and  the  ojjerator  can  by  making 
a  few  changes  in  the  position  of  the  small  chair,  by  mov- 
ing and  readjusting  the  tube  stand  and  the  headrest, 
have  radiographic  access  to  any  part  of  the  oral  cavity 
or  associated  structures.  The  arrangement  of  the  appa- 
ratus preparatory  to  seating  the  patient  is  shown  in 
Fig.  48. 

The  fact  that  this  requires  but  a  few  moments,  does 
not  disarrange  the  office,  or  put  the  patient  to  discom- 
fort, justifies  the  author  in  feeling  that  it  is  by  all  means 
the  preferable  method  for  use  in  the  average  dental  office. 

With  the  head  thus  supported,  as  shown  in  Fig.  49,  the 
rays  are  directed  from  the  opposite  side  of  the  head, 
and,  therefore,  must  pass  through  the  entire  face  or 
skull  in  transit.  The  question  naturally  arises,  how  is 
this  to  be  accomplished  without  superimposing  the  shad- 

*Eisen,  15.  J.,  and  Ivy,  Robert  H. :    American  Journal  of  Roentgenology,  May,   1916. 


DENTAL    AND    ORAL   RADIOGRAPHY    TECHNIC  97 

ows  of  one  side  upon  the  shadows  of  the  other  side,  and 
thereby  producing  a  chaotic  result. 

For  instance,  let  us  suppose  that  we  wish  to  obtain 
a  radiogram  of  the  left  side  of  the  upper  and  lower  jaws 
extending  from  the  cuspid  region  in  front  to  the  angle 
of  the  jaw  behind,  and  from  the  floor  of  the  orbit  above 
to  the  inferior  margin  of  the  mandible  below.  If  we  are 
to  get  a  correct  shadowgraphic  representation  of  this 
area,  it  should  be  free  from  the  shadows  of  the  opjDosite 
side,  and  this  can  only  he  accompUshed  hy  directing  the 
rays  in  such  a  manner  that  they  tvill  miss  the  areas  not 
desired  and  will  pass  through  those  we  wish  to  record. 

In  accomplishing  this,  we  must  take  into  consideration 
two  structures;  viz.,  the  spine  and  the  ascending  ramus 
of  the  mandible  (on  the  right  side  in  this  instance  as 
the  left  side  is  to  be  radiographed)  and  cause  the  rays 
to  pass  in  through  this  opening  and  thereby  reach  the 
desired  area.  The  way  in  which  this  is  accomplished  is 
shown  in  Fig.  50,  A  and  B,  and  Fig.  51,  A  and  B. 

An  important  factor  in  accomplishing  this  is  the  posi- 
tion in  which  the  patient's  head  is  held  as  it  is  pressed 
against  the  plate.  Held  in  the  manner  shoAvn,  the  rays 
can  be  made  to  pass  in  between  the  ascending  ramus  of 
the  mandible  and  the  spine,  and  can  pass  in  at  approxi- 
mately a  perpendicular  direction  to  the  long  axis  of  the 
teeth  and  the  plate,  giving  correct  shadow  lengths  upon 
the  plate.  Fig.  52  shows  a  radiogram  made  by  using  this 
technic. 

If  this  rule  is  disregarded  and  the  rays  passed  through 
the  structures,  as  shown  in  Fig.  53,  A  and  B,  the  shadows 
of  the  opposite  side  will  be  superimposed  upon  the  shad- 
ows of  the  structures  desired,  and  a  chaotic  result  pro- 
duced.    The  result  of  such  technic  is  shown  in  Fig.  54. 

In  a  similar  manner  as  shown  in  Figs.  50  and  51,  with 
slight  adjustments  in  the  position  of  the  plate,  the  head, 


DENTAL    AND    ORAL    RADIOGRAPHY 


Fig.   50-^. 


Fig.   50-B. 

Fig.   50. — Technic  for  left  side.     M-L,   median  line;    S,   the   spine;   A,   ascending   ramus 
and  angle  of  lower  jaw;   P-F,  plate  or  film. 


DENTAT.    AND    OTlATv    RADTOGTIAPTTY    TECIFNIC  91) 


Fig.    51-/1. 


Fig.   Sl-B. 

Fig.  SI. — Technic  for  right  side.     M-L,  median  line;  S,  the  spine;  A,  ascending  ramus 
and  angle  of  lower  jaw;  P-F,  plate  or  film. 


100 


DENTAL   AND    ORAL   RADIOGRAPHY 


and  the  tube,  the  areas  in  the  upper  and  lower  jaws  ex- 
tending from  the  median  line  to  the  first  premolars,  and 
from  the  nose  above  to  the  inferior  margin  of  the  man- 
dible below,  can  be  radiographed  (Fig.  55,  A  and  B). 


Fig.   52. 


Likewise  the  structures  at  the  median  line  including  the 
incisors,  both  above  and  below,  the  anterior  portions  of 
the  mandible  and  maxilla,  the  nasal  cavity  and  its  ac- 
cessory sinuses,  may  be  radiographed  by  passing  the 


DENTAL   AND    ORAL   RADIOGRAPHY    TECHNIC  101 


Fig.    S3-A. 


Fig.  53-B. 

Fig.     S3.— Incorrect    technic.       The    shadows    of    both    sides    will    be     imposed     upon 

the   plate. 


102  DENTAL   AjSTD    OEAL    RADIOGRAPHY 

rays  directly  through  the  skull,  as  sho^^m  in  Figs.  56  and 
57.  In  this  instance,  the  shadow  of  the  spine  will  be 
superimposed  upon  the  dental  structures,  but  owing  to 


Fig.  54. — The  result  of  incorrect  technic.     This  is  a   radiogram  of  the  same  subject  as 

shown    in    Fig.    52. 

the  fact  that  it  is  so  far  removed  from  the  plate,  its 
shadow  does  not  interfere  seriously.  It  is  important,  in 
making  these  pictures,  to  have  the  patient's  head  sup- 
ported in  such  a  manner  that  it  can  be  held  still  for  a 


DENTAL    AND    OIIAL    KADIOGIlArilY    TECirXIC  103 


Fig.  55 -.4. 


Fig.  SS-B. 

I'"ig.  55.  — The  ai-eas  in  the  upper  and  lower  jaws  extending  from  tlie  median  lin< 
lo  Ihc  lirst  premolar  can  Ije  radiographed  by  utilizing  tliis  teehnic.  A,  techiiie  Im 
left    sirle;    B,    teehnic    for   right   side. 


104 


DENTAL   AND    ORAL   RADIOGRAPHY 


longer  period  than  is  required  in  making  the  exposures 
of  the  other  areas  mentioned. 

When  ready  to  make  the  exposure  for  extra-oral  radio- 
grams, the  apparatus  is  arranged  with  the  anode  of  the 
tube  about  twenty  inches  from  the  plate.  The  patient 
is  instructed  to  heep  the  mouth  closed  tvith  the  teeth 
together  in  their  natural  occlusion.  They  should  also  be 
warned  as  to  the  approximate  length  of  time  the  ex- 
posure will  require,  and  that  they  must  remain  perfectly 
quiet. 


Fig.    56. — The    structures    at    the    median   line    including   the    incisors,    both   above   and 
below,   may  be  secured  in   this  way. 


With  the  more  powerful  types  of  apparatus,  extra-oral 
radiograms  require  but  short  exposures,  but  if  an  oper- 
ator does  not  possess  high  power  apparatus,  he  should 
not  hesitate  to  use  this  method,  as  a  patient  properly 
seated  and  supported,  as  shown  in  Fig.  49,  can  easily  re- 
main quiet  for  five  or  ten  seconds,  or  perhaps  even  longer, 
should  it  be  necessary. 

In  making  a  complete  radiographic  examination  of  the 
teeth,  the  maxilla  and  mandible,  the  author  suggests  the 
following  procedure.     Extra-oral  radiograms  should  be 


DENTAL    AND    ORAL   RADIOGRAPHY    TECIIISriC  105 

made  of  each  side,  using  the  technic  ilhistrated  in  Figs. 
50,  51,  and  55.  This  would  mean  two  plates  for  each 
side.  Then  by  the  use  of  intra-oral  films,  the  region  ly- 
ing between  the  cuspids  both  above  and  below,  should  be 
radiographed.  These  plates  and  films  should  then  be 
developed  and  examined.  If  the  procedure  has  been  car- 
ried out  with  due  regard  for  all  the  elements  involved, 
the  result  should  constitute  a  general  radiographic  sur- 


Fig.    57. — In  following  the   technic   illustrated  in   Fig.    56   the   patient's   head   should  be 
supported   by  a   bandage   of   gauze  to   insure  perfect   immobility. 

vey  of  the  teeth,  the  maxilla  and  the  mandible.  Should 
any  of  the  plates  or  films  exposed  fail  to  result  in  good 
radiograms,  additional  exposures  should  be  made,  as 
nothing  but  good  radiograms  should  be  depended  upon 
for  diagnosis. 

It  is  sometimes  advisable  after  making  a  complete  radi- 
ographic examination  by  the  method  just  advocated,  "to 
check  up"  the  findings  of  extra-oral  radiograms  by  the 
use  of  the  intra-oral  films.    For  instance,  suppose  a  large 


106  DEISTTAL   AND    ORAL    RADIOGRAPHY 

plate  shows  what  appears  to  be  an  abscess  upon  the  root 
of  an  upper  bicuspid  or  molar  tooth.  An  intra-oral  radio- 
gram of  this  particular  area  will  often  settle  any  doubts, 
as  a  higher  degree  of  detail  can  often  be  obtained  by  con- 
centrating upon  the  small  area  in  question. 

The  author  would  not  wish  to  impl}^  by  the  preced- 
ing remarks  upon  technic,  that  the  few  rules  enumerated 
constitute  a  safe  and  never  failing  means  of  producing 
good  radiograms.  There  are  many  points  to  be  consid- 
ered which  can  not  be  included  in  so  limited  a  text,  but 
which  must  be  learned  in  the  school  of  experience,  such 
as  the  necessary  variations  from  the  given  rules  of  tech- 
nic because  of  anatomic  variations  in  the  dental  and  oral 
structures  of  patients.  Therefore,  the  rules  of  technic 
which  have  been  presented  must  be  accepted  only  in  the 
light  of  principles. 


CHAPTER  VII 

TECHNIC  OF  DENTAL  AND  ORAL  RADIOGRAPHY 

(Continued) 

Successful  radiography  depends  upon  a  sequence  of 
operations,  each  of  which  must  be  carried  out  with  scien- 
tific accuracy.  These  steps,  upon  which  the  finished  prod- 
uct depends,  may  be  enumerated  as  f oIIoavs  : 

1st — Correct  technic  of  position. 

2nd — Proper  tube  and  current  conditions. 

3rd — Correct  exposure  and  development  of  plates  and 
films. 

It  would  be  difficult  to  determine  which  of  these  steps 
is  the  most  important;  in  fact,  they  are  all  so  important 
that  a  radiogram  is  a  success  or  failure  in  accordance  Avith 
the  degree  of  accuracy  with  which  each  is  carried  out. 
In  the  preceding  chapter,  the  actual  technic  of  radiog- 
raphy, so  far  as  the  arrangement  of  apparatus  is  con- 
cerned and  its  relative  position  to  the  patient  and  the 
plate  (or  film),  has  been  discussed.  We  Avill,  therefore, 
proceed  to  the  next  factor  for  consideration. 

Proper  Tube  and  Current  Conditions 

The  character  of  the  x-rays  produced  in  a  tube  de- 
pends upon  the  degree  of  its  vacuum  and  the  current 
which  passes  through  it.  We  know  that  the  x-rays  are 
produced  by  the  cathode  stream  striking  the  anode  or 
target,  and  that  this  cathode  stream  (Fig.  59-M)  is  gen- 
erated by  the  flow  of  the  current  in  the  tube.  The  veloc- 
ity of  the  cathode  stream  depends  upon  the  voltage  of 
the  current  entering  the  tube,  therefore,  the  higher  the 

107 


108  DENTAL    AND    ORAL   RADIOGRAPHY 

voltage,  the  faster  the  cathode  stream  travels,  and  the 
more  intense  or  penetrating  are  the  x-rays  produced. 
The  quantity  of  x-rays  produced  depends  upon  the  mil- 
liamperage  of  the  current. 

In  considering  the  role  enacted  by  the  voltage  and  mil- 
liamperage  in  the  x-ray  production,  we  have  assumed 
that  the  tube  is  exhausted  to  a  high  degree  of  vacuum, 
for  the  degree  of  vacuum  determines  to  a  large  extent, 
the  value  of  the  other  two  factors.  The  degree  of  vac- 
uum of  a  tube  is  designated  as  high,  medium,  or  low, 
a  "high  tube"  being  one  in  which  the  vacuum  is  well 
nigh  complete;  in  a  ''medium  tube"  the  vacuum  is  less 
complete,  while  a  "low  tube"  is  one  in  which  the  vacuum 
is  far  from  complete. 

For  dental  radiography  a  fairly  high  tuhe  is  indicated, 
as  with  such  a  tube  x-rays  may  be  produced  having  a  de- 
gree of  penetration  sufficient  to  pass  thsough  the  oral 
structures  and  produce  the  desired  effect  upon  the  emul- 
sion of  the  plate  or  film. 

When  a  current  of  high  voltage  is  passed  through 
such  a  tube,  it  should  light  up  in  a  characteristic  man- 
ner forming  two  hemispheres  which  have  a  definite  line 
of  demarcation.  The  hemisphere  in  front  of  the  target 
which  is  the  active  hemisphere,  is  evident  by  a  fluores- 
cence deep  apple  green  in  color,  while  the  other  hemi- 
sphere should  be  evident  by  a  lack  of  greenish  light. 

To  Determine  the  Vacuum  of  a  Tube 

The  comparative  degree  of  vacuum  of  a  tube  can  be 
determined  in  the  following  manner :  Connect  the  tube 
to  the  x-ray  machine  as  shown  in  Fig.  58.  See  that  the 
third  terminal  {S')  is  moved  well  away  from  the  nega- 
tive terminal  {S),  or  better  still,  disconnect  the  wire  run- 
ning to  the  regulation  chamber  {R).  Now,  move  the 
sliding  rods  {B  and  D)  of  the  secondary  spark  gap,  to- 


DENTAL   AND    ORAL   RADIOGRAPIIY    TECTINIC 


109 


ward  each  other  until  they  are  ahout  three  inches  apart, 
and  start  the  current.  Unless  the  tube  is  loiu,  the  cur- 
rent will  jump  the  spark  gap  instead  of  passing  through 
the  tube.  If  the  tube  resists  the  current  and  causes  it 
to  jump  the  spark  gap,  it  is  said  to  have  "backed  up" 
three  inches  of  spark.    Thus  a  "low  tube"  will  back  up 


two  or  three  inches  of  spark,  a  "medium  tube"  five  or 
six  inches,  while  a  high  tube  will  back  up  six  or  eight 
inches.  In  fact,  the  vacuum  of  a  tube  may  be  so  great 
that  only  the  most  powerful  x-ray  machines  will  operate 
it.  Such  a  tube,  however,  is  not  useful  for  dental  radiog- 
raphy. 

The  vacuum  of  a  tube  may  also  be  determined  by  the 
use  of  an  instrument  known  as  a  milliampereineter. 
This  instrument  which  is  usually  an  accessory  of  either 
the  induction  coil  or  transformer,  is  connected  in  circuit 
with  the  tube,  and  measures  the  current  passing  through 
the  tube.    With  a  "low  tube"  the  milliamperemeter  will 


110  DENTAL   AND    ORAL   RADIOGRAPHY 


show  a  reading  of  15  to  18,  while  with  a  "medium  tube" 
the  reading  will  be  from  10  to  12,  and  with  a  ' '  high  tube ' ' 
the  milliamperemeter  will  register  5  or  less. 

Relative  Merits  of  Low,  Medium,  and  High  Tubes 

A  low  tube  under  average  current  conditions  gives  a 
clear  sharp  hemisphere  of  pale  greenish  light  in  front  of 
the  target,  with  usually  a  trace  of  bluish  light  in  the  re- 
gion of  the  assistant  anode.  If  the  tube  is  very  low,  the 
cathode  stream  shows  blue,  and  there  is  a  bluish  light 
back  of  the  active  hemisphere.  Such  a  tube  will  not  do 
good  radiographic  work,  as  the  x-rays  produced  by  it 
are  lacking  in  penetration. 

A  "medium  tube"  gives  a  clear,  sharp  hemisphere  of 
light  greenish  color,  and  there  is  an  absence  of  bluish 
light  back  of  the  target.  The  rays  emanating  from  such 
a  tube  are  more  penetrating  than  those  from  the  "low 
tube,"  but  are  not  so  well  suited  for  "bone  radiography" 
as  those  which  come  from  a  tube  fairly  high  in  vacuum. 
When  such  a  tube  is  operating,  it  gives  a  clear  sharp 
hemisphere  deep  apple  green  in  color,  with  a  lack  of 
greenish  light  back  of  the  target.  The  x-rays  emanat- 
ing from  such  a  tube  are  of  degree  of  penetration  ivliich 
is  best  suited  for  hone  radiography,  for  they  penetrate 
and  pass  through  the  soft  tissues  and  to  a  sufficient  de- 
gree through  the  bone  structure  to  give  good  contrast. 

It  is  ver}^  important  that  the  vacuum  of  such  a  tube  be 
kept  uniform,  for  if  it  gets  low,  the  power  of  penetration 
of  the  rays  is  decreased,  and,  on  the  other  hand,  if  the 
vacuum  gets  too  high,  the  penetrating  power  of  the  rays 
will  be  increased,  with  the  result  that  they  will  penetrate 
through  the  bone  structure  as  easily  as  the  soft  tissues. 
Consequently,  unless  very  short  exposures  are  given, 
there  will  be  little  if  any  contrast  and  the  plate  will  be 
dark  and  hazy. 


DENTAL    AND    ORAL    RADIOGllArj  H'    TEC  II  NIC  111 

Reg-ulating"  the  Tube 

Prior  to  seating  and  arranging  the  i:)atient,  the  tube 
should  be  tested  out  and  any  needed  change  in  its  vac- 
uum effected.  This  is  easily  accomplished  by  utilizing 
the  third  terminal  of  the  x-ray  machine.  The  tube  should 
be  connected  to  the  machine  as  sho^vn  in  Fig.  58.  The 
terminals  of  the  regulating  spark  gap  (S'S)  should  be 
placed  about  four  inches  apart,  and  the  current  (of  cor- 
rect working  strength)  turned  on  for  an  instant.  If  a 
line  of  sparks  jum^D  between  S'  and  S,  it  shows  the  vac- 
uum of  the  tube  is  too  high.  In  this  event  the  regulating 
spark  gap  (S'S)  should  be  reduced  to  about  two  inches, 
and  a  small  amount  of  current  turned  on.  This  weaker 
current  will  jjass  across  the  spark  gap  (S'S),  travel  down 
the  wire  connected  to  the  regulating  chamber,  and  by 
heating  the  asbestos  (impregnated  with  chemicals),  will 
liberate  enough  gas  to  reduce  the  vacuum.  Unless  the 
tube  is  very  high,  a  few  seconds  will  suffice  to  reduce  it 
to  the  vacuum  desired.  To  be  sure  the  vacuum  is  right, 
the  regulating  spark  gap  (S'S)  should  be  widened  to 
about  four  inches,  and  the  desired  working  current  again 
passed  through  the  tube  for  an  instant.  If  the  tube  lights 
up  with  a  clear  sharp  active  hemisphere  deep  apple 
green  in  color  with  a  lack  of  greenish  light  back  of  the 
target,  you  then  know  it  is  ready  for  work. 

If  an  x-ray  machine  is  not  equipped  with  a  third  termi- 
nal, the  same  results  in  regulating  the  tube  may  be  ef- 
fected by  using  the  regulating  adjuster  (Fig.  59),  the  end 
of  which  can  be  placed  at  the  desired  distances  from 
negative  wire  near  its  point  of  attachment  to  the  tube. 
The  tube  may  also  be  lowered  by  attaching  the  negative 
wire  directly  to  the  regulating  chamber  and  passing  a 
small  amount  of  current  through  the  circuit. 

These  manipulations  should  be  carried  out  with  the 


112  DENTAL   AND    ORAL    RADIOGRAPHY 

greatest  caution,  for  a  tube  is  an  extremely  delicate  and 
sensitive  piece  of  apparatus  and  ivill  not  stand  abuse. 
A  careless  operator  can  quite  easily  reduce  the  vac- 
uum to  such  a  degree  that  the  tube  is  useless.  Such  a 
tube  has  a  purple  appearance  when  the  current  is  passed 
through  it.  If  such  a  tube  has  not  been  too  greatly 
abused,  it  will  often  regain  its  vacuum  if  given  a  rest.  If 
this  does  not  bring  the  vacuum  up,  it  can  often  be  brought 
back  in  the  following  way:  The  spiral  spring  (Fig.  59) 
connecting  the  anode  and  assistant  anode  should  be  re- 
moved and  the  positive  wire  from  the  machine  attached 


A— Anode. 

U- -Assistant  Anode 

C— Cathode 

D-RcRulat.ng 
ChamlKT 

r-RegulaiinB      Ad- 
juster 

G— Hemispluie 

H-Conneclion 

Wire 
I-Assistani    Anode 
Cap 

K-Anode   fa|. 

l^Cathode    Call 

M— Cathode  Stream 

N-Focal    I'oint 


Fig.     59. 


to  the  assistant  anode  (/).  The  negative  wire  is  at- 
tached as  usual  (at  L)  and  a  light  current  is  run  through 
the  tube  for  a  minute  or  two  at  a  time.  If  this  is  done 
once  or  twice  a  day  for  several  days,  the  vacuum  will 
usually  come  up.  Any  increase  in  vacuum  will  be  indi- 
cated by  the  milliampere  readings  dropping  off,  or  by 
the  increased  length  of  spark  gap  the  tube  will  ''back 


up." 


If  a  tube  does  not  respond  to  this  treatment  but  con- 
tinues to  be  purple  while  operating,  it  indicates  that  it 
is  practically  non vacuous  or  "punctured."  It  is  then 
useless  and  should  be  sent  back  to  the  manufacturer  for 


DENTAL   AND    ORAL   RADIOGRAPHY    TECHNIC  113 

repairs.  In  the  event  a  tnhe  is  "completely  punctured," 
the  current  in  passing  through  it  simply  jumps  the  gap 
])etween  the  anode  and  cathode,  and  is  evident  as  a  line 
of  white  sparks. 

One  tube  complication  not  yet  mentioned  is  sometimes 
encountered  in  the  use  of  induction  coils.  This  is  knoA\Ti 
as  ''inverse  in  the  tube,"  and  is  the  result  of  the  pres- 
ence of  inverse  current  (current  in  the  wrong  direction) 
in  the  secondary  circuit  of  the  coil.  "Inverse"  is  evi- 
dent in  the  tube  by  the  appearance  of  rings  of  light  back 
of,  and  usually  running  at  an  angle  to,  the  active  hemi- 
sphere, or  by  a  fullness  of  greenish  light  back  of  the  ac- 
tive hemisphere,  with  rings  about  the  assistant  anode. 

Inverse  current  in  a  tube  will  generate  secondary  rays 
which  have  the  tendency  to  make  the  outline  of  the  image 
on  the  plate  hazy  or  "less  sharp,"  as  these  rays  are  pro- 
duced in  the  tube  elsewhere  than  at  a  focal  point  on  the 
target.  It  also  produces  heat  in  the  tube  which  lowers 
the  vacuum  and  hence  lessens  the  penetration  of  the  rays 
coming  from  it. 

"Inverse"  in  the  tube  can  usually  be  controlled  or  pre- 
vented by  the  use  of  "  a  multiple  spark  gap  "  or  "  a  valve 
tube"  arranged  in  series  with  the  x-ray  tube,  and  by 
using  a  tube  which  is  fairly  high  in  vacuum.  If  it  still 
persists  after  these  precautions  are  taken,  it  indicates 
an  imperfect  adjustment  of  the  induction  coil  or  some  of 
its  accessories. 

All  manufacturers  of  x-ray  tubes  furnish  full  instruc- 
tions as  to  the  care  of  and  manner  of  using  x-ray  tubes. 
These  instructions  should  be  carefully  read  and  explic- 
itly foUoived. 

In  order  that  uniform  results  may  be  obtained,  it  is 
advisable  to  always  use  the  tube  at  the  same  vacuum, 
with  the  same  amount  of  current.  The  proper  "working 
current"   may   be    determined   in   the   following   way: 


114  DENTAL    AND    ORAL    RADIOGRAPHY 

With  the  tube  disconnected,  set  the  sliding  rods  {B  and 
D  of  Fig.  58)  of  the  machine  about  six  inches  apart. 
Then  start  the  current  in  the  machine,  and  beginning 
with  a  low  current  increase  it  until  a  fat  fuzzy  "cater- 
pillar spark"  is  produced  across  the  spark  gap.  As 
soon  as  this  spark  or  discharge  appears,  the  switch 
should  be  pulled  out,  but  the  rheostat  or  other  control- 
ling apparatus  left  as  it  was  when  the  spark  appeared, 
so  that  Avhen  the  tube  is  connected,  the  proper  working 
current  will  come  from  the  machine. 

The  tube  should  then  be  connected  up  and  given  a  trial. 
If  it  is  not  too  high  in  vacuum,  it  should  take  the  cur- 
rent, or  in  the  event  it  is  too  high,  it  Avill  "back  up"  the 
spark,  and  the  discharge  instead  of  passing  through  the 
tube  will  jump  the  gap.  If  the  tube  requires  regulating, 
it  can  be  done  by  the  methods  before  described. 

With  the  working  current  and  vacuum  established,  it 
is  a  good  idea  to  separate  the  sliding  rods  on  the  ma- 
chine to  at  least  eight  inches,  to  insure  against  the  tube 
backing  up  the  current,  for  in  the  event  the  tube  should 
start  going  up  during  the  time  the  exposure  is  being 
made,  the  startling  noise  made  by  the  discharge  jumping 
the  gap,  may  cause  the  patient  to  move  and  thereby  blur 
the  radiogram.  If  several  exposures  of  five  or  ten  sec- 
onds each  are  made,  the  tube  should  be  given  sufficient 
rest  between  exposures  so  that  it  will  not  heat  up.  This 
is  important. 

With  proper  tube  and  current  conditions,  the  length  of 
time  required  for  the  exposure  will  depend  upon  the  t^^pe 
of  x-ray  machine  used,  and  the  thickness  and  density  of 
the  parts  to  be  radiographed,  varying  with  different  pa- 
tients according  to  age  and  structural  make  up. 


CHAPTER  ^^III 

CORRECT   p]XPOSURE  AND  DEVELOP:\rENT  OF 
X-RAY  PLATES  AND  FILMS 

X-ray  plates  and  films  differ  from  those  used  in  or- 
dinary photography  in  that  their  emulsion  is  more  sen- 
sitive and  better  adapted  to  record  the  shadows  jorodueed 
b}^  the  x-ray.  Therefore,  they  should  ahva3's  be  used  in 
preference  to  ordinary  plates  and  films. 

The  same  general  photographic  rules  apply  to  x-ray 
plates  and  films  as  apply  to  the  ordinary  kind,  except 
perhaps  that  they  demand  a  greater  degree  of  accuracy 
and  care  throughout  the  process  of  exx)osure  and  devel- 
opment, if  the  very  best  results  are  to  be  obtained. 

X-ray  Plates 

X-ray  plates  are  supplied  by  the  manufacturers,  packed 
in  lightproof  boxes  containing  one  dozen  plates.  They 
are  obtainable  in  any  desired  size,  but  for  dental  and 
oral  radiograph}^,  a  5x7  plate  is  large  enough.  If  stored 
in  the  laboratory,  they  should  be  kept  in  a  lead-lined  box 
prior  to  their  preparation  for  exposure,  or  they  will  be- 
come ''fogged,"  as  lightproof  boxes  offer  no  protection 
whatever  from  the  x-ray. 

A  suitable  plate  and  film  storage  box  is  shown  in  Fig. 
60.  Such  a  box  should  be  about  twelve  inches  square 
and  five  inches  deep.  This  will  enable  the  storage  of 
several  boxes  of  5x7  plates,  and  in  addition,  three  or  four 
dozen  dental  films. 

In  their  preparation  for  exposure,  each  plate  is  placed 
in  two  lightproof  envelopes,  one  of  which  is  black  and 

115 


116 


DENTAL   AND    ORAL,   EADIOGRAPHY 


the  other  red  or  orange  in  color.  Such  envelopes  are 
furnished  by  plate  manufacturers  and  are  obtainable  in 
the  desired  size.  The  transference  of  the  plate  from  its 
original  box  to  the  envelopes  must,  of  course,  only  he  done 
in  the  photographic  darkroom.  The  plate  is  first  slipped 
into  the  smaller  envelope  which  is  usually  the  black  one, 
with  the  emulsion  side  of  the  plate  facing  the  smooth 
side  of  the  envelope  (the  side  free  from  seams  or  over- 
lapping edges).  The  envelope  containing  the  plate  is 
then  placed  in  the  larger  or  yellow  envelope,  flap-end 
first,  with  the  smooth  side  of  the  inner  envelope  facing 
the  smooth  side  of  the  outer  one.     Plates  prepared  in 


X-rayproof   film   and  plate   chest. 


this  way  are  then  ready  for  exposure  and  can  be  placed 
back  in  the  lead-lined  box  until  needed. 

In  "loading  these  envelopes,"  care  should  be  taken 
lest  the  emulsion  of  the  plate  become  scratched,  as 
scratches  even  though  they  be  very  slight  will  often  cur- 
tail the  value  of  the  finished  radiogram. 

It  is  not  advisable  to  keep  large  quantities  of  plates 
loaded  in  envelopes,  unless  they  are  to  be  used  within  a 
few  days,  as  the  contact  of  the  paper  with  the  emulsion 
will  in  time  affect  it  adversely. 

All  "brands"  of  x-ray  plates  are  not  the  same,  there- 
fore, if  the  best  results  are  obtained  in  using  any  par- 


DEVELOPMENT    OF    PLATES   AND    FILMS  117 

ticular  kind,  they  must  be  handled  in  strict  accordance 
with  the  manufacturers'  instructions.  For  dental  and 
oral  radiography,  a  plate  should  be  fairly  rapid  (that  is, 
it  should  not  require  a  long  exposure),  give  a  high  de- 
gree of  detail  and  good  contrast,  and  should  be  uniform 
in  its  reaction  to  the  x-ray. 

X-ray  Films 

In  making  intra-oral  radiograms,  a  film  is  preferable 
to  a  plate  as  it  is  flexible  and,  therefore,  can  be  more 
easily  adapted  to  the  inside  of  the  mouth.  These  films 
are  obtainable  in  several  convenient  sizes,  wrapped  in 
lightproof  and  dampproof  coverings  ready  for  expos- 
ure. Like  plates  they  should  be  kept  in  a  lead-lined  box 
for  protection. 

With  these  "dental  films"  as  they  are  called,  you  have 
the  choice  of  two  different  emulsions,  one  of  which  is 
much  more  ' '  rapid ' '  than  the  other. 

The  "rapid"  or  "fast  film"  requires  only  about  one- 
fourth  or  one-third  as  long  an  exposure  as  the  "regular" 
or  "slow  film,"  and  therefore  is  an  advantage  to  the 
radiographer  who  uses  one  of  the  less  powerful  types 
of  x-ray  machines.  However,  such  a  film  does  not  have 
as  much  latitude  as  the  slow  film,  and  is  therefore  more 
apt  to  be  overexposed.  If  properly  exposed,  either  one 
will  give  satisfactory  results. 

When  arranging  a  plate  or  film  for  exposure,  the  emul- 
sion side  should  lie  next  to  the  structures  being  radio- 
graphed. If  this  rule  is  systematically  followed,  it  is  an 
easy  matter  to  identify  radiograms,  i.  e.,  whether  they 
represent  structures  on  the  right  or  left  side  of  the  me- 
dian line. 

Development  of  Plates  and  Films 

The  process  of  "development"  of  either  plates  or 
films  may  be  briefly  described  as  follows:     At  a  con- 


118  DENTAL   AND    ORAL   RADIOGEAPHY 

venient  time  following  the  "exposure,"  the  plate  or 
plates  (or  films)  are  taken  into  the  ''darkroom."  Such 
a  room  has  all  white  light  excluded  from  it,  and  is  illu- 
minated only  by  a  so-called  "ruby  light"  or  darkroom 
lantern.  The  darkroom  should  be  supplied  with  a  shelf 
or  table  about  two  and  a  half  feet  wide  and  three  feet 
long  placed  at  ordinary  table  height  from  the  floor,  so 
that  the  operator  may  sit  ujoon  a  stool  while  at  work. 
Upon  this  shelf  there  should  be  four  trays,  one  for  the 
"developing  solution,"  one  for  the  "fixing  bath,"  and 
the  other  two  for  water.  Where  a  darkroom  is  supplied 
with  running  water  and  a  sink,  only  three  trays  are  nec- 
essary. 

With  all  light  excluded  from  the  room  except  the  ruby 
light  coming  from  the  darkroom  lantern,  the  plate  (or 
film)  is  taken  out  of  its  envelope  and  immersed  emulsion 
side  up  in  the  developing  solution.  In  order  to  insure  a 
uniform  action  by  the  developer,  the  tray  should  be  fre- 
quently rocked  Avith  a  gentle  motion.  If  the  plate  (or 
film)  has  been  properly  exposed,  development  should  be 
complete  in  about  five  minutes  (although  the  time  varies 
with  different  formulae). 

The  plate  or  film  is  then  removed  from  the  developer 
and  placed  in  a  tray  of  water  to  thoroughly  wash  the 
developing  solution  from  it.  This,  of  course,  requires 
but  a  moment,  and  it  is  then  immersed  in  the  "fixing 
bath,"  keeping  the  emulsion  side  up.  As  soon  as  the 
plate  has  been  in  the  fixing  bath  a  few  seconds,  the  dark- 
room door  may  be  opened  and  light  admitted  without  in- 
jurious effects.  However,  the  plate  (or  film)  must  still 
remain  in  the  fixing  bath  until  it  has  "cleared"  (until 
all  milkiness  is  gone  from  the  back  of  the  plate),  which 
will  usually  require  from  five  to  ten  minutes.  In  fact, 
it  is  better  to  let  it  "fix"  for  at  least  five  minutes  longer 
than  is  required  for  it  to  become  clear. 


DEVELOPMENT    OF    PLATES    AND    FILMS  119 

When  the  fixing  process  is  complete,  the  plate  must  be 
placed  in  water  and  thoroughly  washed  to  remove  all  the 
fixing  solution  from  it.  This  can  he  accomplished  hy 
washing  it  in  several  changes  of  water,  or  better  still, 
place  it  in  a  basin  or  tray  of  cold  "running  water"  for 
ten  or  fifteen  minutes. 

When  the  washing  process  is  complete,  the  emulsion 
side  of  the  plate  or  film  should  be  gently  rubbed  with  a 
clean  piece  of  wet  cotton,  holding  the  plate  (or  film) 
under  a  cold  water  faucet  during  the  act.  The  developed 
radiogram  is  then  ready  to  dry.  Plates  should  be  stood 
on  edge  or  placed  in  a  suitable  rack  so  that  nothing  Avill 
come  in  contact  with  the  emulsion  side,  and  left  until 
perfectly  dry.  Films  may  be  pinned  to  the  edge  of  a 
shelf,  or  secured  to  a  line  with  suitable  clips.  The  drying 
process  should  take  place  in  a  room  free  from  dust  or 
soot,  for  these  will  prove  injurious  to  the  drying  emulsion. 

The  size  of  the  trays  used  in  the  darkroom  will  depend 
upon  the  number  of  plates  or  films  which  are  to  be 
carried  through  the  developing  process  at  a  time.  For 
plates,  the  author  uses  trays  8x10  inches  in  size.  With 
such  trays  two  5x7  plates  can  be  carried  through  at  a 
time.  Where  a  large  number  of  plates  are  being  devel- 
oped, additional  trays  can  be  used  and  if  necessary 
"tanks"  capable  of  holding  a  dozen  plates,  utilized  in 
the  fixing  or  washing  process.  In  developing  "dental 
films, ' '  small  trays  Avill  be  found  convenient,  and  unless  a 
large  number  are  to  be  developed  at  a  time,  a  4x5  or  5x7 
tray  will  be  large  enough. 

Trays  should  be  labeled  according  to  the  purpose  for 
which  they  are  to  be  used,  and  used  for  that  purpose 
only.  That  is,  developing  trays  should  be  used  for  the  de- 
veloper only,  and  fixing  trays,  only  for  the  fixing  bath, 
if  troublesome  chemical  reactions  are  to  be  avoided. 
Any  one  of  several  good  formulae  may  be  used  in  the 


120  DENTAL   AND    OKAL   EADIOGKAPHY 

developing  and  fixing  process.  The  following  has  given 
satisfactory  results  in  the  hands  of  the  author,  and  is 
easily  prepared: 

Developer 

Water   (distilled)  20  oz. 

Metol  20  gr. 

Hydroquinone  80  gr. 

Sodium  sulphite   (dry)  1  oz. 

Sodium  carbonate  (dry)  1  oz. 

Potassium  bromide  10  gr. 

Fixing  Bath 
Solution  A: 

Water  (distilled)  30  oz. 

Hyposulphite  of  soda  1  lb. 

Solution  B: 

Water  (distilled)  15  oz. 

Chrome  alum  1  oz. 

Sodium  sulphite  (dry)  2  oz. 

Solution  C: 

Water   (distilled)  5  oz. 

Sulphuric  acid  (C.P.)  %  oz. 

Add  C  to  B  (when  cold)  and  the  mixed  solutions  to  A. 

If  the  best  results  are  to  be  obtained  in  developing, 
the  temperature  of  the  solution  should  be  kept  between 
65°  and  75°  F.  If  the  temperature  gets  much  over  75°, 
the  plate  will  develop  too  fast,  while  if  the  temperature 
goes  much  below  65°,  development  mil  be  retarded. 

It  is  a  mistake  to  try  to  develop  a  large  number  of 
plates  with  the  same  mixture  of  developer,  for  after  it 
has  developed  a  half  dozen  plates,  it  will  become  weak 
and  not  give  the  best  results.  Therefore,  do  not  hesitate 
to  use  plenty  of  fresh  developer  if  you  expect  to  get  satis- 
factory results. 


DEVELOPMENT    OF    PLATES    AND    FILMS  121 

The  same  rule  applies  to  the  fixing  solution.  It  must 
be  fresh  and  clean  to  give  good  results. 

Under  proper  tube  and  current  conditions,  and  with 
correct  length  of  exposure,  a  plate  should  require  about 
five  minutes  for  its  development.  An  overexposed  plate 
will  not  require  so  long,  while  an  underexposed  plate  mil 
require  a  longer  time. 

To  get  the  most  out  of  a  plate,  it  should  be  developed 
until  fairly  dense,  that  is,  until  it  is  about  the  same  color 
on  each  side.  If,  after  it  has  cleared  in  the  fixing  bath, 
it  appears  too  dark  or  dense,  you  know  that  it  has  been 
overexposed.  Therefore,  in  making  subsequent  expo- 
sures decrease  the  length  of  exposure.  If,  upon  clear- 
ing, the  image  on  the  plate  is  faint  and  indistinct,  you 
have  reason  to  think  it  has  been  underexposed.  There- 
fore, increase  the  length  of  exposure. 

By  keeping  the  tube  and  current  conditions  right,  the 
approximate  length  of  exposure  for  any  given  case  is 
easily  determined  by  the  operator,  after  a  little  experi- 
ence. As  stated  before,  this  mil  depend  upon  the  t3rpe 
of  x-ray  machine  used,  the  thickness  and  density  of  the 
parts  to  be  radiographed,  and  the  age  and  structural 
make  up  of  the  patient. 


CHAPTER  IX 

THE  INTERPRETATION  OF  DENTAL  AND 
ORAL  RADIOGRAMS 

The  ability  to  correctly  interpret  dental  and  oral  ra- 
diograms is  an  accomplishment  which  every  dentist 
should  possess.  In  fact,  it  should  be  viewed,  not  only  in 
the  light  of  an  accomplishment,  but  as  a  requisite  of 
modern  dentistry. 

Unfortunately,  the  assertion  is  not  infrequently  made 
by  certain  ill-informed  members  of  the  dental  profession 
that  only  minor  importance  should  be  attached  to  the 
findings  of  the  radiogram,  their  claim  being  that  such 
images  can  be  construed  as  showing  conditions  which  do 
not  actually  exist. 

Such  an  attitude  can  be  explained  as  being  the  out- 
growth of  several  things,  among  which  a  lack  of  knowl- 
edge of  the  fundamental  principles  of  radiography  and 
its  various  branches,  and  especially  of  the  science  of  in- 
terpretation, stands  as  an  important  factor.  Therefore, 
opinions  of  the  x-ray  and  its  application  in  dentistry  ex- 
pressed by  those  unqualified,  should  not  be  regarded 
seriously. 

The  idea  also  seems  to  prevail  in  the  dental  profes- 
sion that  the  interpretation  of  radiograms  is  an  ex- 
tremely simple  matter,  requiring  little  if  any  prepara- 
tion on  the  part  of  the  one  who  is  to  make  the  interpre- 
tation. This  erroneous  idea  is  doubtless  responsible, 
not  only  for  many  errors  being  committed,  but  also  for 
a  lack  of  greater  appreciation  b}^  the  profession  of  the 
value  of  the  radiogram. 

122 


INTERPJlETATIOISr    Oi-'    HA1JI0(JIIAMS  123 

The  first  requisite  of  interpretation  is  an  accurate 
hnoivledge  of  the  anatomy  and  physiology  of  the  struc- 
tures involved,  for  a  radiogram  is  a  shadoiv  picture,  and 
a  shadoiv  picture  is  meaningless  unless  one  is  thoroughly 
familiar  ivith  the  main  characteristics  of  the  original. 

The  radiogram  may  be  said  to  vary  from  an  ordinary 
shadow  picture,  as,  in  addition  to  mere  outlines,  varying 
densities  are  shown  due  to  the  fact  that  the  x-ray  pene- 
trates all  matter  in  inverse  ratio  to  its  mass  or  density. 

If  one  is  possessed  of  an  accurate  knowledge  of  the 
anatomy  and  physiology  of  the  dental  and  oral  struc- 
tures, the  next  step  toward  acquiring  the  ability  to  cor- 
rectly interpret  radiograms  of  these  structures,  would 
be  to  become  familiar  ivith  their  radiographic  appear- 
ance under  normal  conditions,  for  unless  one  be  familiar 
with  the  appearance  in  the  radiogram  of  the  structures 
under  normal  conditions,  it  is  obviously  impossible  to  in- 
telligently recognize  pathologic  or  anomalous  conditions 
unless  they  were  of  a  glaring  nature. 

When  we  speak  of  the  radiographic  appearance  of  the 
structures  under  normal  conditions,  we  refer,  not  only 
to  a  freedom  from  pathologic  or  anomalous  involvement, 
but  also  to  the  character  of  the  radiogram  itself,  which 
must  be  normal  in  that  it  must  he  made  in  accordance 
ivith  a  technic  which  results  in  the  shadows  of  the  struc- 
tures under  scrutiny  being  imposed  upon  the  plate  or 
film  in  their  correct  proportions. 

Therefore,  it  is  essential  that  in  addition  to  the  before 
mentioned  requisites,  one  who  would  intelligently  inter- 
pret radiograms  must  understand  enough  of  the  funda- 
mental rules  of  radiographic  technic  to  know  when  ex- 
amining a  radiogram,  ivhether  or  not  the  technic  in- 
volved in  its  making  ivas  correct  or  fcmlty,  and  if  fcmlty, 
whether  or  not  the  degree  of  faidt  is  sufficient  to  render 
it  so  inaccurate  as  to  be  useless. 


124 


DENTAL   AND    OEAL    RADIOGRAPHY 


In  correctly  made  radiograms,  the  dental  and  oral 
structures  under  normal  conditions  have  a  characteristic 
appearance,  for,  owing  to  the  var^dng  densities  of  the 
contained  structures  in  our  field,  they  appear  upon  the 
plate  or  film  in  a  manner  most  advantageous  for  obser- 
vation. For  instance,  it  will  be  noted  upon  the  examina- 
tion of  such  a  radiogram,  that  metallic  fillings,  if  they 
are  present,  appear  as  white  masses,  and  root  fillings  as 
somewhat  less  dense  lines.  The  enamel  and  dentin  are 
next  in  density,  while  root  canals  show  plainly  as  dark 
channels  in  the  dentin,  and  the  alveolar  process  and  max- 
illse  show  their  fine  uniform  cancellous  structures  in  vari- 


#    r    ^ 


A.  B. 

Fig.  61. — The  radiographic  appearance  of  the  teeth  and  their  surrounding  struc- 
tures under  normal  conditions  are  here  shown.  A,  upper  bicuspids  and  molars;  B, 
lower  molars. 


ous  degrees  of  density,  depending  upon  their  thickness. 
(See  Fig.  61.) 

In  examining  a  radiogram,  it  is  essential  that  the 
original  plate  or  film  only  be  used,  and  this  should  be 
examined  carefully  and  in  a  proper  light,  if  the  maximum 
amount  of  information  is  to  be  obtained  from  it. 

This  is  best  accomplished  by  utilizing  some  sort  of 
illuminating  box  or  cabinet  from  which  varied  degrees 
of  light  are  obtainable.  The  face  of  such  a  cabinet 
should  be  covered  with  ground  glass,  so  that  the  light 
transmitted  will  be  equally  distributed  and  free  from 
shadows.    As  a  radiogram  is  a  transparency,  a  dim  light 


INTERPRETATIOiSr    OF    RADIOGRAMS  125 

behind  it  will  bring  out  one  set  of  shadows  to  their 
greatest  clearness.  An  increase  in  the  light  will  show 
forth  still  other  effects ;  while  a  high  degree  of  illumina- 
tion will  bring  out  the  more  dense  portions. 

In  this  manner  each  portion  of  the  radiogram  may  be 
studied  under  a  degree  of  light  destined  to  bring  out  the 
maximum  amount  of  detail. 

Now  with  a  ''print"  or  "lantern  slide"  one  can  study 
the  field  only  from  a  one  light  aspect  and  oftentimes  in 
order  to  secure  any  detail  in  the  higher  or  less  dense 
areas,  it  will  be  found  that  the  dense  areas  must  be 
printed  almost  to  an  inky  blackness.  This  fact  accounts 
for  the  unsatisfactory  appearance  of  many  radiograms 
used  as  illustrations  in  our  journals,  for  when  reduced 
to  halftone  engravings,  much  of  their  valuable  detail  is 
lost. 

In  examining  intra-oral  radiograms,  it  is  an  advan- 
tage to  place  them  in  a  film  mount  which  will  hold  them 
securely  and  render  it  unnecessary  to  view  them  while 
being  held  between  the  fingers.  Such  a  "mount"  should 
preferably  be  made  of  celluloid  Avith  one  side  clear  and 
the  other  side  dull,  which  allows  the  light  transmitted 
to  be  of  the  same  character  as  that  coming  through 
ground  glass. 

If  one  be  unfamiliar  with  the  fundamental  rules  of  ra- 
diographic technic,  he  can  not  know,  when  examining  a 
radiogram,  just  what  portions  of  it  are  to  be  relied  upon 
to  give  dependable  information,  for  as  a  rule,  owing  to 
anatomic  arrangement  of  the  structures  in  our  field,  only 
limited  areas  can  be  relied  upon  to  be  "in  focus"  in  each 
radiogram.  But  if  one  is  possessed  of  an  accurate 
knowledge  of  the  anatomy  and  physiology  of  the  parts 
involved,  understands  the  fundamental  rules  of  radio- 
graphic technic,  and  is  familiar  with  the  appearance  in 
the  radiogram  of  the  dental  and  oral  structures  under 


126  DENTAL   AND    ORAL   RADIOGRAPHY 

normal  conditions,  it  should  hy  no  means  he  difficult  to 
see  any  alterations  or  changes  ivhich  occur  in  these  struc- 
tures as  a  residt  of  anomalous  or  pathologic  conditions. 

The  mere  ability  to  note  an  alteration,  or  change,  in 
the  structures  does  not  fulfill  the  requirements  of  intelli- 
gent interpretation,  for  these  alterations,  or  changes, 
can  have  their  full  significance  only  to  one  ivho  under- 
stands the  pathologic  conditions  which  may  develop  in 
these  structures,  and  the  character  of  the  anatomic 
changes  ivhich  they  bring  about.  Therefore,  it  should 
be  apparent  that  the  ability  to  intelligently  interpret  ra- 
diograms is  not  a  thing  to  be  acquired  overnight,  but 
must  come  as  the  result  of  study  in  several  important 
branches,  and  anyone  who  attempts  it  otherwise  as- 
sumes responsibilities  unworthily. 

Assuming  that  you  are  familiar  with  the  appearance 
in  the  radiogram  of  the  dental  structure  under  normal 
conditions,  let  us  consider  some  of  the  changes  to  be 
found  in  the  presence  of  anomalous  and  pathologic  con- 
ditions. 

As  a  tooth  is  much  more  dense  than  the  boiry  struc- 
tures of  the  jaw  or  adjacent  parts,  any  anomaly  of  form, 
size,  or  position,  is  easily  discernible  even  though  it  oc- 
cupy a  position  far  from  what  might  be  expected;  as, 
for  instance,  in  the  case  of  impacted  molars,  teeth  in  the 
antrum,  etc.     (See  Fig.  62.) 

Likewise,  and  for  the  same  reason,  the  presence  in, 
or  absence  from,  the  jaws  of  successors  of  the  deciduous 
teeth  can  easil}^  be  determined,  as  Avell  as  the  state  of 
development  of  any  unerupted  tooth  (Fig,  63). 

Fractured  roots  or  fractures  of  the  bone  even  with- 
out displacement,  are  often  discernible  at  the  line  of 
fracture,  owing  to  the  fact  that  the  line  of  fracture  of- 
fers less  resistance  to  the  penetration  of  the  ra^^^s,  and, 
therefore,  is  apparent  upon  the  plate  as  a  dark  line. 


INTERPRETATION    OF    RADIOGRAMS 


12' 


Fig.    62. — A   cuspid   tooth    lying   against   the   anterior   wall    of    the    antrum, 
noted   that  the  cuspid   is  inverted  in   its   position. 


It    will   be 


.  iMg.  63. — A  radiogram  to  determine  the  state  of  dentition  of  the  right  side  in 
the  mouth  of  a  child  eleven  years  old.  The  developing  second  molars  are  shown, 
likewise  the  upper  second  bicuspid  and  the  lower  first  bicu.^iiid  about  to  erupt.  It 
will  be  noted  that  the  lower  second  deciduous  molar  has  no  successor,  nor  is 
there  an  upper  first  bicuspid   present  in  the  jaw. 


128 


DENTAL   AND    ORAL   RADIOGRAPHY 


In  examining  radiograms,  we  should  bear  in  mind  the 
fact  that  very  dense  tissues  are  characterized  by  white 
areas,  while  less  dense  tissues  appear  darker,  and  the 
absence  of  tissue  is  indicated  by  blackness.  To  avoid 
confusion,  we  should  remember  that  in  ordinary  negative 
photographic  prints,  this  color  spectacle  is  reversed.* 


Fig.    64. 


Fig.    65. 


Fig.   64. — An  alveolar   abscess  involving  the  roots  of  an  tipper  central  incisor  and 
lateral  incisor.      No   root   canal   fillings  are   present   in   either  tooth. 

Fig.  65. — There  is  evidence  of  a  small  alveolar  abscess  about  the  apex  of  the 
root  of  the  first  bicuspid,  while,  a  larger  one  is  shown  to  exist  about  the  apex  of 
the    second   bicuspid. 


Fig.   66. 
Fig.   66. — Ivarge  alveolar  abscess   about  the   root  of   a  lower  first  bicuspid. 


One  of  the  most  characteristic  alterations  or  changes 
in  the  tissues  to  be  noted  in  the  radiogram,  is  that  to  be 
found  where  an  alveolar  abscess  is  present.  We  know 
that  when  such  an  abscess  takes  place  there  is  always 
an  accompanying  destruction  of  the  cancellous  bone  tissue 


*In  this   text   positive   prints   have   been   used   so   as   to   reproduce   as   nearly   as   pos- 
sible   the    color    spectacle    of    radiograms. 


INTERPIlKTATrON    OF    RADIOGRAMS 


129 


at  the  immedito  seat  of  tlie  innammatory  process.  Know- 
ing that  the  absence  of  tissue  is  indicated  in  the  radio- 
gram by  a  dark  or  black  area,  such  an  area  if  located 
at  the  apex  of  a  devitalized  tooth,  or  about  a  root  or  frag- 
ment of  a  root,  would  indicate  the  presence  of  an  alve- 
olar abscess.  In  fact,  where  these  dark  areas  are  found 
in  the  alveolar  process,  and  are  not  natural  cavities,  such 
as  the  antrii,  or  nasal  cavities,  or  such  well-defined  nerve 


B. 


C. 


Fig.  67. — A  shows  an  upper  bicuspid  tooth  with  an  alveolar  abscess  at  its  root 
apex.  It  will  be  noted  that  the  root  canal  is  improperly  filled.  B  shows  the  same 
tooth  about  two  months  after  it  was  treated  and  the  root  canal  properly  filled.  The 
rarefied  area  about  the  apex  has  greatly  decreased  in  size.  C  shows  the  same  tooth 
about  six  weeks  later.  The  abscess  area  has  entirely  disappeared  and  the  bone 
structure   about   the   apex    appears   to    be    normal. 


openings  as  the  mental  foramina,  and  where  they  are 
markedly  circumscribed,  that  is  having  a  distinct  and 
abrupt  line  of  demarcation  between  the  dark  area  and  its 
surrounding  tissue,  we  can  in  nearly  every  case,  even  if 
a  clinical  history  be  lacking,  make  the  positive  diagnosis 
of  alveolar  abscess.     (See  Figs.  64,  65  and  66.) 


130 


DENTAL    AlStD    ORAL   RADIOGRAPHY 


Not  infrequently,  dentists  are  prone  to  disregard  such 
evidence,  as  these  areas  are  often  to  be  fomid  about  the 
apices  of  teeth  giving  no  inflammatory  symptoms.  How- 
ever, in  the  light  of  our  present  knowledge  of  these 
conditions,  we  know  that  this  fact  no  longer  carries 
weight,  nor  is  it  worthy  of  special  consideration.  The 
fact  remains,  as  indicated  in  the  radiogram,  that  a 
change  has  taken  place  in  the  structures,  and  such 
changes  occur  only  as  a  result  of  the  presence  of  an  in- 
flammatory process.  Furthermore,  it  has  been  demon- 
strated that  when  such  inflammatory  processes  are  really 


rig.  6S. 


Fi.s 


Fi-  68— 'Small  abscesses  are  shown  at  the  apices  of  two  upper  bicuspid  teelh. 
If  in°making  the  radiogram  the  images  of  the  teeth  had  been  lengthened  as  the  re- 
sult  of   incorrect   technic,   these   areas   would   not  be   discernible. 

Fig.   69. — A   necrotic   area   about  the   roots   of   an  upper   central   and  lateral. 

eliminated,  the  cancellous  tissues  involved  will  again  re- 
gain their  normal  character.     (See  Fig.  67.) 

Alveolar  abscesses  do  not  by  any  means  present  a 
"stereotyped"  appearance  in  the  radiogram,  but  vary 
greatly  in  size.  For  this  reason,  the  smaller  ones  may 
sometimes  be  overlooked,  or  not  be  regarded  seriously 
by  those  lacking  the  requisites  of  intelligent  interpreta- 
tion. Likewise,  these  small  abscesses  may  sometimes  not 
be  apparent  in  the  radiogram  as  a  result  of  the  employ- 


INTEEPRETATIOiN"    OF    r.ADIOGRAMS 


131 


nient  of  incorrect  teclmic  in  the  exposure  of  the  plate 
or  film.     (Fig.  68.) 

Necrosis  likewise  appears  upon  the  plate  as  a  dark 
area,  but  differs  in  a  characteristic  way  from  the  or- 
dinary alveolar  abscess  in  that  it  is  not  circumscribed; 


Fig.  70. — A  necrotic  area  lying  below  a  lower  cuspid.  It  will  be  noted  that  there 
is  not  a  distinct  and  abrupt  line  of  demarcation  between  the  light  area  and  its  sur- 
rounding tissue  as  is  the  case  with  alveolar  abscesses,  but  the  area  gradually  shades 
off  from  light  into  dark. 


namely,  that  there  is  not  a  distinct  and  abrupt  line  of 
demarcation  hetiveen  the  dark  area  and  its  surrounding 
tissue,  as  is  the  case  with  the  circumscribed  infections, 
but  the  area  gradually  shades  off  from  dark  into  light, 
portraying  the  progessive  characteristics  of  this  disease. 
(See  Figs.  69  and  70.) 


132 


DENTAL   AND    ORAL   EADIOGRAPHY 


The  different  filling  materials  vary  but  little  in  rela- 
tive graduation  of  density,  and  when  used  as  root  filling 
materials,  are  plainly  visible  as  light  lines.  Because 
they  differ  in  density  from  cementum  and  dentin,  the 


rig.    71.  Fig.    72. 

Fig.    71. — Root   canal   fillings   in   a  lower   first  molar. 

Fig.    72. — Root    canal    filling    material    forced    beyond    the    root    apex    of    an    upper 
second   bicuspid. 


Fig.    73. 


Fig.    74. 


Fig.  73. — A  steel  wire  introduced  into  the  root  canal  to  determine  its  length.  It 
has  passed   through  the  apex  and   entered   the   antrum. 

Fig.  74. — A  destructive  process  involving  the  pericemental  and  alveolar  tissues 
about   an   upper    first   bicuspid. 


Fig.  73. — Characteristic  appearance  of  the  enveloping  tissues  about  the  upper  bi- 
cuspids and  molars  in  a  well-developed  case  of  pyorrhea  alveolaris.  Compare  the 
condition   shown   here   with   that   shown   in   Fig.    61-A    and   B. 


INTERPRETATION    OF    RADIOGRAMS  133 

extent  to  which  they  have  been  introduced  into  the  root 
canals  is  easily  discernible.     (See  Figs.  71  and  72.) 

Broken-off  broaches  and  other  instruments,  or  small 
wires  introduced  into  root  canals  to  determine  their 
length  or  the  extent  to  which  they  have  been  opened,  be- 


Fig.   76. — An  osteosarcoma  of  the  mandible. 


Fig.    77. 


Fig.    78. 


•  i^l-^'    77.— -Well-developed    cyst    over    an    upper    lateral    incisor.      Root    filling    mate- 
rial   forced   through    the    ape.x    of    the    lateral   incisor    is    plainly    visible. 
Fig.    78. — Well-developed    cyst   lying   below   the    lower   incisors. 


134  DENTAL,   AND    ORAL   KADIOGEAPHY 

cause  of  their  great  density,  appear  very  white  and  are 
easily  differentiated  from  root  canal  fillings  or  tooth 
structure.     (See  Fig.  73.) 

Where  a  destructive  process  has  ensued  in  the  peri- 
dental membrane,  or  in  the  bony  wall  of  the  alveolus 
(pyorrhea  pockets)  and  is  present  on  the  mesial  or  distal 
side  of  a  tooth,  these  conditions  appear  upon  the  plate 
as  dark  areas  owing  to  the  fact  that  the  rays  pass 
through  them  more  easily,  and  effect  the  emulsion  of  the 
plate  to  a  greater  degree  than  if  normal  bone  structure 
is  present.  The  approximate  extent  of  the  destructive 
process  is,  therefore,  easily  determined.  (Figs.  74  and 
75.) 

Cyst  and  tumors  of  the  maxilla  or  mandible,  owing  to 
the  fact  that  the  character  of  the  changes  they  bring 
about  renders  the  areas  involved  less  dense,  are  visible 
upon  the  plate  as  a  dark  area.     (Figs.  76,  77  and  78.) 

In  seeking  out  the  various  anomalies  and  pathologic 
conditions  to  which  the  teeth  and  oral  structures  are 
subject,  ive  should  not  he  misled  hy  indefinite  shadoivs 
upon  the  x-ray  plates.  The  very  nature  of  these  struc- 
tures, their  gross,  as  well  as  minute,  anatomy,  renders 
them  somewhat  difficult  to  radiograph,  and  necessitates 
a  refinement  of  technic  greater  than  that  demanded  with 
most  of  the  other  portions  of  the  human  anatomy. 
Therefore,  only  radiograms  made  in  accordance  ivith  a 
definite  and  exacting  technic  should  he  relied  upon  for 
diagnosis.  If  a  douht  exists  in  any  given  instance,  an  ad- 
ditional or  even  several  more  exposures  should  he  made, 
so  that  any  conclusions  reached  will  he  founded  upon 
definite  evidence. 


CHAPTER  X 

INDICATIONS  FOR  THE  USE  OF  THE  X-RAY 
IN  THE  PRACTICE  OF  DENTISTRY 

Prior  to  the  discovery  of  the  x-ray  and  its  adoption  in 
dental  practice,  the  diagnosis  of  many  abnormal  condi- 
tions in  the  alveolar  process  and  in  the  maxilla  or  mandi- 
ble proper  had  to  be  accomplished,  or  at  least  attempted 
by  the  dentist  largely  by  relying  upon  his  "judgment" 
and  "experience."  As  these  excellent  attributes  are  not 
infallible,  the  progessive  members  of  the  profession  were 
quick  to  recognize  in  the  x-ra}^  a  veritable  godsend,  be- 
cause it  rendered  more  positive  and  accurate  than  here- 
tofore, the  diagnosis  of  many  pathologic  conditions.  It 
has  also  aided  just  as  materiall}^  in  prognosis  and  treat- 
ment. In  fact,  so  indispensable  has  it  become  that  if 
the  dentist  attempts  certain  operations  without  its  aid, 
he  assumes  unworthily  his  professional  responsibilities. 

In  enumerating  the  many  instances  where  this  agent 
should  be  used,  the  author  will  not  attempt  to  give 
preference  or  importance  to  any  particular  field,  or  to 
classify  the  indications  in  the  order  of  their  frequency 
of  occurrence,  for  this  will  depend  largely  upon  the 
character  of  practice  enlisting  the  efforts  of  different 
men.  When  the  need  arises  for  its  use,  it  should  he 
used  whether  the  need  arises  in  the  practice  of  the  or- 
thodontist, prosthedontist,  oral  surgeon,  or  general 
practitioner,  etc.,  for  the  obligation  is  the  same  if  the 
dentist  expects  to  do  his  full  duty  b}^  his  patients. 

For  Purposes  of  General  Oral  Examination 

Not  infrequently  the  dentist  is  consulted  by  patients 
who  are  undergoing  no  discomfort  or  pain  from  their 

135 


136  DENTAL   AND    ORAL   RADIOGRAPHY 

teeth,  but  realizing  their  importance  as  etiologic  factors 
of  systemic  disease,  wish  to  midergo  a  thorough  exami- 
nation. In  many  instances,  such  an  examination  will  not 
be  complete  without  a  radiographic  survey  of  the  mouth. 
Especially  is  this  true  where  such  patients  have  pulpless 
teeth,  or  where  large  fillings,  bridge  work  or  crowns 
are  present.  Notwithstanding  the  fact  that  often  the 
clinical  history  of  such  cases  reveals  nothing  that  will 
lead  the  dentist  to  believe  that  active  septic  foci  have 
existed  in  such  mouths,  the  radiographic  examination 
should,  nevertheless,  be  made,  for  in  the  light  of  our 
present  knowledge,  it  must  be  concluded  that  these  con- 
ditions frequently  exist  without  subjective  or  objective 
symptoms. 

Such  examinations  are  particularly  important  in  the 
case  of  patients  suffering  from  some  systemic  conditions, 
who  are  referred  by  a  physician  to  determine  whether  or 
not  the  teeth  are  an  etiologic  factor. 

Where  such  an  examination  reveals  no  active  septic 
foci,  but  shows  the  presence  of  one  or  several  pulpless 
teeth  with  root  canal  fillings  which  do  not  measure  up 
to  the  full  requirements  of  such  fillings,  it  is  important 
that  such  teeth  be  resubjected  to  radiographic  examina- 
tion at  regular  intervals  to  see  whether  or  not  they  re- 
main in  a  healthy  state. 

Radiographic  Requirements. — In  order  to  do  justice 
to  such  cases,  extra-oral  radiograms  should  be  made  of 
each  side.  These  should  show  the  upper  and  lower  teeth 
and  adjacent  structures  posterior  to  the  cuspids.  Intra- 
oral radiograms  of  the  upper  and  lower  incisors  and 
cuspids  should  also  be  secured,  and  the  whole  series  de- 
veloped and  examined.     (See  Fig.  79.) 

Where  the  extra-oral  radiograms  show  suspicious 
areas  about  the  teeth  which  do  not  show  with  sufficient 
clearness  to  meet  the  demands  of  diagnosis,  intra-oral 


INDICATIONS    FOR    X-RAY    IN    DENTISTRY  137 

radiograms  may  then  ho  made  of  these  areas,  as  a  means 
of  confirmation.  (See  Fig.  80.)  Some  operators  prefer 
to  use  the  intra-oral  method  entirely,  in  making  a  general 
examination,  hut  this,  in  the  author's  opinion,  is  a  mis- 
take, for  the  reason  that  all  areas  of  pathologic  impor- 
tance are  not  accessible  to  these  small  films. 


Fig.  79. — Extra-oral  radiogram  of  the  right  side  made  for  piirposes  of  general  ex- 
amination. Suspicious  areas  are  to  be  seen  above  the  upper  first  bicuspid  and  about 
roots  of  the  lower  second  molar.     An   unerupted  upper  third  molar  is  also  visible. 

To  Determine  the  Seat  of  Pericemental  Infections 

Not  infrequently  it  is  a  difficult  matter  to  determine 
the  tooth  responsible  for  a  pericemental  infection  or  an 
alveolar  abscess,  as  the  inflammatory  process  may  be  in 
progress  in  the  region  of  several  teeth,  each  of  Avhich 
may  be  under  suspicion,  or  the  infected  area  may  be  at 
a  point  remote  from  the  suspected  tooth.  A  radio- 
grapliic  examination  will  quickly  settle  all  doubts,  for  the 
radiogram  will  reveal  the  source  and  determine  whether 


138 


DENTAL   AND    ORAL    RADIOGRAPHY 


or  not  one  or  more  teeth  are  involved.  •>  It  will  likewise 
show  the  extent  to  which  the  periapical  tissnes  have  be- 
come involved  and  will  often  shed  valuable  information 
on  the  prognosis  of  the  case.     (See  Figs.  81,  82  and  83.) 


Fig.   80. 


Fig.  81. 


Fig.    SO. — Intra-oral  radiogram  used   as   a   means  of   confirmation   of  the   findings   of 
the   extra-oral    radiogram. 

Fig.   81. — Alveolar  abscesses   are   shown   to  be  present  at  "the  apex   of  each   bicuspid 
root. 


Fig.    82. 


Fig.    83. 


Fig.   82. — Upper  bicuspid  teeth  with  abscesses. 

Fig.  83. — Severe  inflammatory  process  in  progress  about  an  upper  lateral  incisor. 
The   root   end   shows   a   mariced   hypercementcsis. 

Radiographic  Requirements. — Intra-oral  radiograms 
will  usually  suffice.  Where  the  lower  molars  and  bicus- 
pids are  under  examination,  and  the  tissues  under  the 
tongue  are  very  tender,  the  extra-oral  method  can  be  used 
to  advantage,  if  the  patient's  comfort  is  a  consideration. 
(See  Fig.  84.) 


INDICATIONS    rOR   X-RAY    IN    DENTISTRY  139 

Root  Canal  Treatment 

Of  the  various  dental  operations,  there  is  none  that  is 
more  nniversally  in  need  of  further  elucidation  than  the 
treatment  and  filling  of  root  canals.  As  generally  prac- 
ticed at  the  present  time,  this  work  can  easily  be  termed 
the  "greatest  shortcoming  of  dentistry."  To  those  who 
recognize  the  uncertainty  of  results  in  this  field,  and  the 
serious  results  which  accompaii}^  failure  to  render  sterile 


Fig.    84. — E.xtra-oral   radiogram    of   the   lower  molars   showing   the   presence   of   a   large 

alveolar  abscess. 

and  to  com^Dletely  fill  root  canals,  the  x-raA^  offers  indis- 
pensable aid. 

Before  considering  the  treatment  of  a  tooth  (or  teeth), 
a  radiogram  should  be  made  to  show  the  topography  of 
the  roots  to  be  treated.  If  these  are  proved  to  be  ana- 
tomically within  the  range  of  treatment,  an  attempt  may 
then  be  made  to  remove  all  organic  material  from  the 
canals  and  to  open  them  up  to  the  very  apical  foramen. 
Fine  diagnostic  wires  should  then  be  inserted  and  car- 
ried to  the  end  of  the  canal,  or  as  far  as  the  operator  has 


140 


DE^TTAL   AZCD   OEAL  EADIOGBAPHY 


been  able  to  iDtroduce  the  broaches.  After-  sealing  them 
in  with  gutta  percha,  a  second  radiogram  shonld  be 
made.  Becanse  of  their  greater  density,  the  Tores  will 
show  distinctly  in  the  radiogram  and  will  enable  the 
operator  to  determine  to  what  extent  the  canal  or  canals 
have  been  opened.  It  will  likewise  determine  whether 
any  opening  leading  from  the  pnlp  chamber  is  a  canal  or 
a  perforation. 


Vig.  85. — A^  two  c;;tr 
teeth  with  the  ramal'i  cl££^ 
after  tlie  root  ranala  hare 


:tly  Slled  canals;  B,  the  same 
s  in  place;   C,  the  same  teeth 


liVhen  the  canals  are  open  to  the  end  (as  shown  by 
the  inserted  wires)  and  the  necessary  treatment  and 
sterilization  has  been  completed,  the  root  canal  fillings 
can  then  be  inserted.  Another  radiogram  should  tlien 
be  made  to  determine  whether  or  not  the  root  fillings  ex- 
tend to  the  apical  foramina  and  seal  the  canals.  If  they 
do  not.  thev  shonld  be  removed  and  the  before-men- 


INDICATIONS    FOR    X-RAY    IN    DENTISTRY 


141 


c. 

Fig.    86. — A,    lower   second    bicuspid    needing   root    canal    treatment    and    filling;    B, 
same  tooth  with  canal  cleaned  out  and  diagnostic  wire  in  place;   C,  same  tooth  with 

the  root  canal   filled. 


B. 


C. 

Fig.  87. — A,  an  upper  first  bicuspid  needing  root  canal  treatment  and  filling;  B,  canals 

have   been   cleaned   out  and   diagnostic   wires  put   in   place;    C,   canals   filled. 


142 


DEISTTAL   AiSTD    OEAL    RADIOGRAPHY 


tionecl  operative  and  .roentgenographic  process  repeated 
until  success  is  obtained. 

Even  when  all  precautions  are  taken  and  results  seem 
eminently  satisfactory,  several  radiograms  should  be 
made  at  regular  intervals  of  from  three  to  six  months 
following  the  filling  of  .the  roots,  to  determine  whether 
or  not  the  operation  has  been  successful,  so  far  as  the 
periapical  tissues  are  concerned.     This  is  especially  im- 


C.  D. 

-A,   showing   condition   present;    B,   diagnostic   wires   inserted;    C,   root   canals 
filled;   D,   resection   of   roots. 


portant  where  roots  have  been  the  seat  of  periapical  in- 
fections prior  to  the  time  when  treatment  was  inaugu- 
rated.   (See  Figs.  85,  86  and  87.) 

Radiographic  Requirements. — Intra-oral  radiograms 
exclusively  should  be  used  for  this  work.  An  excep- 
tion might  be  made  in  the  case  of  the  lower  molars  and 
bicuspids,  if  the  tissues  under  the  tongue  are  sufficiently 


INDICATIONS    FOR    X-RAY    IX    DENTISTRY  14d 

tender  to  make  the  placing  of  the  fihiis  for  exposure  a 
hardship  to  the  patient.  Excellent  extra-oral  radio- 
grams of  tliis  area  may  be  obtained,  providing  the  opera- 
tor has  the  ability  and  constancy  to  master  the  neces- 
sary technic. 

Root  Resection 

Where  root  resection  is  contemplated,  the  intelligent 
dentist  should  first  obtain  accurate  radiograms  of  the 


t'       t 


A. 


C. 

I'ig.  89.— -^4,  upper  central  incisor  before  resection;  B,  radiogram  made  immedi- 
a.ely  following  resection;  C,  radiogram  made  after  several  months,  showing  regen- 
eration   of   osseous   tissue. 

roots  under  consideration.  These  aid  him  greatly,  pri- 
marily in  determining  whether  or  not  a  resection  is  in- 
dicated, and  if  it  is,  it  will  give  him  a  fairly  concrete  idea 
of  the  field  of  operation  as  well  as  the  extent  of  the  root 
to  be  resected;  secondarily,  in  determining  whether  or 


144 


DENTAL    AjS^D    OEAL    RADIOGEAPHY 


not  the  root  canal  has  been  sufficiently  well  filled  so  that 
the  filling  extends  past  the  point  where  resection  is  to 
take  place. 

Following  root  resection,  a  radiogram  should  he  made 
as  a  matter  of  record  and  be  used  for  purposes  of  com- 
parison as  the  process  of  healing  progresses.  Subse- 
quently, additional  radiograms  should  be  made  every 
three  months  to  determine  whether  or  not  the  process 
of  bone-regeneration  is  progressing  in  a  satisfactory 
manner.     (See  Figs.  88,  89  and  90.) 


A.  B. 

Fig.   90. — A,  an  upper  central  root  before  resection;   B,  the  same   root  six  weeks  after 
resection,    showing   partial    regeneration. 

Radiographic  Requirements. — Intra-oral  radiograms 
should  be  used  exclusively.  In  fact,  the  necessity  for 
anything  else  could  hardly  arise,  as  root  resection  is 
usually  confined  to  the  anterior  teeth. 

For  Purposes  of  Examination  and  Diagnosis  in 
Pyorrhea  Alveolaris  and  Allied  Diseases 

A  radiographic  examination  of  the  teeth  and  their  in- 
vesting structures  is  of  great  advantage  in  diagnosis  and 
treatment.  In  the  first  place,  accurately  made  radio- 
grams will  often  show  the  extent  to  which  the  destruc- 


INDICATIONS    FOR    X-RAY    IN    DENTISTRY 


145 


tive  process  lias  progressed,  especially  if  areas  of  ab- 
sorption and  ''pockets"  exist  npon  the  mesial  or  distal 
aspects  of  teeth.  Even  where  such  areas  are  visible 
to  the  eye,  the  radiogram  serves  an  important  function 
in  acquainting  the  patient  with  the  true  state  of  affairs, 
thereby  securing  the  patient's  cooperation  in  the  treat- 
ment.    (See  Fig.  91.) 


Fig.    91. — A    well-developed    case   of   pyorrhea    alveolaris   involving   the    molars   and    in- 
cisors.     (After   Arthur   H.    Merritt.) 

When  the  destructive  process  is  sho^\T.i  to  be  exten- 
sive about  certain  teeth,  the  operator  can  more  safely 
judge  whether  or  not  the  treatment  of  such  teeth  should 
be  attempted  or  whether  they  should  be  extracted. 

Where  suppuration  is  occurring  at  the  gingival  margin, 
the  radiogram  is  often  indispensable  in  helping  to  deter- 
mine (by  showing  the  contents  of  the  root  canals) 
whether  the  adjacent  teeth   are  vital,   and  if  nonvital 


146  DENTAL   AK^D    ORAL   RADIOGRAPHY 

whether  or  not  the  suppuration  is  clue  to  a  chronic  alveo- 
lar abscess. 

In  cases  of  gingival  irritation  about  crowned  teeth  or 
teeth  carrying  large  fillings  or  inlays,  a  radiogram  will 
reveal  jagged  or  overhanging  edges,  the  removal  of  which 
is  so  essential  if  the  tissues  are  to  be  restored  to  health. 

Finally,  the  radiogram  or  a  series  of  radiograms  will 
be  of  value  after  active  treatment  has  been  completed, 
to  determine  whether  or  not  the  destructive  process  has 
been  successfully  checked. 

Radiographic  Requirements. — Intra-oral  radiograms 
will  suffice  for  such  cases,  as  pockets  seldom  extend  be- 
low the  apical  area  of  the  roots.  Such  radiograms  should 
be  made  in  series,  so  that  no  area  about  the  teeth  is  left 
unsurveyed. 

In  Crown  and  Bridgework 

Where  teeth  are  to  be  crowned  individually,  or  as 
bridge  abutments,  the  radiogram  will  give  valuable  in- 
formation, not  only  as  to  the  length  and  shape  of  the 
roots,  and  the  condition  of  the  investing  structures,  but 
also  as  to  that  of  the  periapical  tissues.  Where  the  neces- 
sity for  the  devitalization  of  such  teeth  occurs,  the  op- 
erator can  also  judge  by  the  shape  and  condition  of  the 
roots  whether  or  not  the  prognosis  for  successful  root 
treatment  and  filling  is  favorable. 

Where  ^'posts''  are  to  be  placed  in  the  roots,  their 
extent  and  direction  can  be  noted,  and  Avhere  the  ana- 
tomic peculiarities  of  such  roots  make  them  liable  to 
perforation,  precautions  for  avoiding  such  calamities 
may  be  taken. 

Where  spaces  are  to  be  bridged,  and  the  exact  status 
of  the  area  which  is  to  lie  beneath  the  bridge  is  not 
known,  a  radiogram  should  be  made  to  be  sure  that  un- 
erupted  teeth  or  root  fragments  are  not  present.  (See 
Figs.  92,  93  and  94.) 


INDICATIOlSrS    FOR    X-RAY    IN    DENTISTRY 


147 


Radiographic  Requirements. — Intra-oral  radiograms 
are  indicated  for  this  character  of  work. 

Reflexes  of  Obscure  Origin 

Where  painful  reflexes  occur  about  the  face  or  head, 
and  a  clinical  examination  does  not  immediately  deter- 
mine their  possible  origin,  a  radiographic  examination 
of  the  teeth  and  their  adjacent  structures  is  indicated. 
Where  such  reflexes  are  the  result  of  unerupted,  im- 


Fig.   92.  Fig.   93. 

Fig.  92. — An  unerupted  cuspid  tooth  making  an  attempt  to  erupt  under  a  bridge. 
The   patient   was   twenty-eight   years   of   age. 

Fig.  93. — Radiogram  made  to  be  sure  no  root  fragments  were  present  in  the  tis- 
sues  under   the    bridge. 


Fig.   94. — Inflammatory   process   under  a  small   bridge.     An  extensive   pocket   is   shown 
upon   the  mesial  aspect   of  the   root  of  the  bridge   abutment. 

l^acted,  or  anomalous  teeth,  the  presence  of  an^^  of  these 
is  quickly  demonstrated.  Likewise,  if  the  reflexes  are 
caused  by  an  alveolar  abscess,  its  presence  can  be 
thereby  determined. 

Where  pulp  stones  are  producing  the  trouble,  they  can 
often  be  detected,  if  intense  care  is  exercised  in  making 


148  DENTAL   AND    ORAL   RADIOGRAPHY 

the  radiograms.  If  these  reflexes  are  the  result  of  "hid- 
den caries,"  the  radiogram  will  frequently  suggest  the 
presence  of  such  a  condition,  providing  the  cavities  occur 
upon  the  mesio-or  disto-approximal  surfaces  of  the  teeth, 
and  are  sufficiently  extensive  so  that  the  density  of  the 
tooth  structure  in  the  region  of  the  cavity  is  decreased, 
or  the  contour  of  the  tooth  is  altered. 

Radiographic  Requirements. — Approximately  the 
same  plan  of  examination  should  be  used  as  where  a 
general  radiographic  examination  of  the  mouth  is  made ; 
viz.,  extra-oral  radiograms  of  each  side  with  intra-oral 
radiograms  of  the  anterior  teeth.  These  can  be  further 
augmented  with  confirmatory  intra-oral  radiograms,  if 
necessary.    (See  Figs.  79  and  80.) 

In  Oral  Surgery 

Perhaps  the  most  frequent  indication  for  the  use  of 
the  x-ray  in  oral  surgery  occurs  in  cases  in  which  the 
extraction  of  certain  teeth  is  necessary.  For  instance, 
if  one  or  more  third  molars  are  to  be  removed,  a  radio- 
gram of  these  teeth  and  their  surrounding  structures 
will  acquaint  the  operator  with  any  abnormalities  of  po- 
sition or  formation,  and  will  make  it  possible  to  proceed 
with  the  operation  without  unknown  handicaps. 

Following  the  removal  of  teeth,  a  radiogram  of  the 
field  of  operation  is  often  of  value  as  a  matter  of  record, 
to  make  sure  that  no  root  fragments  or  bone  fragments 
are  left  remaining. 

Where  necrotic  areas  are  to  be  curetted,  a  radiogram 
not  only  aids  greatly  in  confirming  the  diagnosis,  but 
gives  the  operator  a  more  comprehensive  idea  of  the 
extent  to  which  the  curettement  must  be  carried  out.  As 
a  postoperative  precaution,  the  radiogram  is  also  fre- 
quently of  value,  especially  where  the  process  of  healing 
does  not  progress  in  a  manner  satisfactory  to  the  pa- 


INDICATIONS    ron    X-EAY    IN    DENTISTRY  149 


Fig.   95-A. 


Fig.   95-B. 
Fig.    95. — Extra-oral    radiograms    of   impacted    and    unerupted    tliird    molars. 


150 


DENTAL   AND    OKAL    RADIOGRAPHY 


tient  or  operator.  Such  postoperative  radiograms  are 
particularly  advantageous  where  patients  move  from  one 
locality  to  another,  and,  therefore,  must  change  surgeons. 

In  handling  fractures  of  the  mandible,  the  x-ray  is 
seldom  necessary  for  purposes  of  diagnosis,  but  it  can 
often  be  used  to  advantage,  and  in  some  instances,  is  quite 
indispensable.  As  a  postoperative  precaution  it  should 
be  used  so  that  no  doubt  may  arise  as  to  the  proper 
placement  of  the  fractured  parts. 

Where  fractures  of  the  maxilla  occur,  a  radiogram  may 
be  of  value  as  a  means  of  confirming  the  clinical  diag- 
nosis. 


A.  B. 

Fig.    96. — Intra-oral    radiograms    of    impacted    lower    third    molars.       Such    radiograms 
are  not  as  satisfactory  as  those  made  by  the   method  shown  in   Fig.   95. 


Where  C3^sts  or  tumors  are  suspected,  the  radiogram 
will  confirm  the  clinical  findings,  and  comprehensively 
outline  the  field  of  operation.  Following  operations  for 
the  relief  of  those  conditions,  radiograms  should  be  made 
at  frequent  intervals  to  determine  whether  or  not  the 
process  of  healing  is  progressing  satisfactorily. 

In  gunshot  wounds  about  the  face  or  mouth,  properly 
made  radiograms  will  localize  the  bullets  or  shot,  and 
thereby  aid  in  their  removal,  as  well  as  in  determining 
the  extent  of  injury  to  the  osseous  structures. 

AVhere  drills,  hypodermic  needles  or  other  instruments 
are  broken  off  and  left  remaining  in  the  tissues,  they  may 


INDICATIONS    FOR    X-llAY    IN    DENTISTRY 


101 


Fig.  97-A. Ivarge  cyst  in  the  mandible  lying  below  a  molar  tooth. 


Fig.    97-B.— Same    case    six    months    after    curettement,    showing    partial    regeneration 
of  the  osseous  structure. 


152 


DENTAL   AND    ORAL   RADIOGRAPHY 


be  easily  located  by  correctly  made  radiograms,  and  their 
removal  rendered  more  certain. 

Radiographic  Requirements. — Both  the  extra-oral  and 
intra-oral  radiograms  are  indicated  in  this  field.  For 
impacted  third  molars,  the  extra-oral  method  is  best,  as 
it  will  clearly  show  not  only  the  third  molar,  but  its  re- 
lationship to  all  other  adjacent  structures.  In  the  case 
of  single-rooted  teeth,  snch  as  incisors,  cuspids,  etc., 
where  hypercementosis  is  suspected,  the  intra-oral 
method  will  prove  adequate.     (See  Figs.  95,  96  and  97.) 


Fig.    98. — Large   abscess   with   cyst   formation   involving  the    upper   central,   lateral    and 

cuspid    roots. 

Where  a  curettement  is  to  be  carried  out,  intra-oral 
radiograms  will  prove  sufficient,  provided  the  field  is  not 
large  (Fig.  98.) 

In  fractures  of  the  mandible,  the  extra-oral  method 
should  always  be  used,  so  that  the  entire  field  in  the  re- 
gion of  the  fracture  can  be  visualized. 

For  fractures  of  the  maxilla,  intra-oral  radiograms 
will  usually  suffice. 

In  the  Practice  of  Orthodontia 

The  necessity  for  using  the  x-ray  in  orthodontic  prac- 
tice varies  with  different  patients,  bat,  generally  speak- 


INDICATIO]\TS    FOIl    X-P.AY    IX    DENTISTRY 


153 


Fig.    99. — This    radiogram    reveals    the    fact    tliat    there    is   a    congenital    aljsence    of    per- 
manent   molars    on    the    left    side. 


Fig.    100. — This   radiogram    reveals   the   fact  that  all   but   one   of   the   permanent   molars 
are   congenitally   absent   on   the   right   side. 


154  DENTAL   AND    ORAL   RADIOGRAPHY 

ing,  may  be  summarized  under  ten  different  headings  as 
follows : 

1.  As  a  means  of  determining  the  presence  or  ab- 
sence of  ufierupted  permanent  teeth  before  treatment  is 
undertaken. 

The  majority  of  patients  requiring  orthodontic  treat- 
ment usually  have  a  mixed  dentition ;  viz.,  the  deciduous 
molars  and  cuspids  are  usually  present.  It  is  essential, 
therefore,  to  determine  whether  or  not  these  deciduous 
teeth  have  their  permanent  successors.  If  the  upper  and 
lower  incisors  have  erupted,  information  concerning  the 
other  permanent  teeth  is  easily  obtained  by  making  a 
radiogram  of  each  side  by  the  extra-oral  method.  Such 
radiograms  are  shown  in  Figs.  99  and  100. 

Such  radiograms  give  the  operator  a  very  adequate 
survey  of  these  unerupted  teeth,  and  leave  no  doubt  as  to 
their  presence  or  absence. 

2.  As  a  means  of  determining  the  approximate  size 
of  unerupted  teeth,  for  luhich  space  must  be  made  in  the 
arches. 

Where  the  deciduous  molars  or  cuspids  have  been  shed 
prematurely,  with  the  usual  resultant  loss  of  space  in  the 
arch,  the  radiogram  can  be  made  to  show  quite  accurately 
the  amount  of  space  which  it  will  be  necessary  to  pre- 
pare for  the  unerupted  teeth.  (See  Figs.  101,  102,  and 
103.) 

3.  To  determine  the  state  of  development  of  unerupted 
teeth  ivhich  are  tardy  in  their  eruption. 

Not  infrequently  permanent  teeth  fail  to  erupt  when 
expected.  By  utilizing  the  radiogram,  their  state  of  de- 
velopment is  easily  determined,  and  often  the  cause  for 
their  noneruption  is  determined.  Steps  can  then  be  taken 
to  open  up  spaces  and  to  hold  them  until  such  a  time  as 
the  teeth  involved  progress  in  their  development  to  the 
point  of  eruption.     (See  Fig.  104.) 


INDICATIONS    FOR    X-IIAY    IN    DENTISTIIY 


155 


Fig.    101. — Unerupted  lower   second   bicuspid  for  which   space   must  be  made  to   permit 

its   eruption. 


ig.    102. — Unerupted   cuspid    for   which    space    must   be    made    if   it   is    to    erupt    in    its 

normal   position. 


156 


DENTAL   AND   OEAL   EADIOGEAPHY 


Fig.  103. — Unerupted  lower  lateral  incisor  for  which  space  must  be  made. 


Tig.    104. — Unerupted  lower  second   molar   prevented   from   erupting  through   impaction 
against   the   lower   first  molar. 


INDICATrOXS    FOR    X-RAY    IN    DENTISTRY 


157 


4.  To  determine  the  approximate  direction  in  ivhich 
teeth  are  erupting  and  the  relationship  ivhich  they  ivill 
hear  to  the  line  of  occlusion  ivhen  erupted. 

Where  the  deciduous  teeth  have  been  retained  in  the 
mouth  longer  than  the  normal  time  and  Avhere  the  roots 
of  these  teeth  have  not  been  entirely  absorbed,  the  erupt- 
ing permanent  teeth  will  sometimes  be  deflected  from 


Fig.    105. — Unerupted    upper   bicuspid   teeth    which   are   being   deflected    to    the    lingual. 


A.  B. 

Fig.    106. — Unerupted    bicuspid    teeth    which    are   rotated    and    erupting   to    the    lingual. 

their  normal  course.  It  is  an  advantage  to  know  the  di- 
rection in  which  they  are  deflected,  so  that  if  retaining 
appliances  are  to  be  placed,  they  may  be  arranged  in 
such  a  way  and  in  such  a  relationship  to  the  erupting 
teeth  that  they  will  not  interfere  with  them.  In  fact, 
it  is  sometimes  possible  to  construct  the  retainer  in  such 
a  way  that  the  tooth  which  is  deflected  from  its  course 
may  be  guided  towards  its  normal  position  or  moved 


158 


DENTAL   AND    ORAL   RADIOGRAPHY 


A. 


B. 


C. 


Fig.  107. — A,  unerupted  cuspid;  B,  same  tooth  after  the  removal  of  the  lateral 
incisor  and  the  deciduous  cuspid  showing  the  attachment  for  moving  the  unerupted 
tooth;    C,   cuspid  tooth   moved   down   to   the   point   of  eruption. 


A. 


B. 


Fig.    108. — A,    two    supernumerary    incisors    are    present  with    the    normal    central 

lying  above  them;   B,  the   same  case   after  the   extraction   of  the   supernumerary   teeth. 

An    attachment    has    been    made    to    the    central    preparatory  to    moving    it    down    into 
place.      The   patient   was    fourteen    years    of    age. 


INDICATIONS    FOR    X-RAY    IN    DENTISTRY  159 

there  before  the  inclined  planes  of  the  opposing  teeth  he- 
come  a  factor  in  estahlishing  it  entirely  out  of  its  normal 
position.    (See  Figs.  105  and  106.) 

5.  As  a  guide  ivhere  it  is  necessary  to  make  attach- 
ments to  unerupted  teeth,  to  aid  in  their  eruption. 

While  it  is  not  often  necessary  to  secure  attachments 
to  teeth  lying  beneath  the  gingival  tissues,  the  occasion 
for  this  sometimes  arises,  as  shoAvn  in  Figs.  107  and  108. 
In  such  cases,  radiograms  should  be  made  as  a  guide  in 
securing  the  attachment.  After  the  attachment  is  se- 
cured, others  should  be  made  to  determine  the  direction 
in  which  force  should  be  applied  to  accomplish  the  desired 
tooth  movement. 

6.  To  determine  the  most  opportune  time  for  the  ex- 
traction of  the  deciduous  teeth. 

Where  the  deciduous  tooth  persists  in  the  mouth,  and 
shows  no  sign  of  being  shed,  it  is  an  advantage  to  deter- 
mine the  extent  of  absorption  of  the  roots,  as  well  as  the 
development  of  its  successor,  so  that  if  extraction  is  re- 
sorted to,  it  can  be  done  with  the  knowledge  that  the  de- 
veloping tooth  will  not  be  disturbed  or  injured,  and  that 
the  successor  has  reached  a  degree  of  development  Avhich 
will  insure  its  eruption  within  a  reasonable  time.  (See 
Figs.  109  and  110.) 

7.  To  observe  the  movement  of  the  roots  of  teeth  and 
their  relationship  to  other  roots  and  structures. 

In  the  bodily  movement  of  teeth,  and  particularly  of 
th€  incisors,  it  is  important  in  young  subjects  that  these 
roots  do  not  encroach  upon  each  other  or  upon  other 
teeth;  for  instance,  an  unerupted  cuspid.  It  is  there- 
fore, advisable,  where  any  doubt  exists,  to  determine  the 
exact  status  of  this  relationship.    (See  Fig.  Ill,  A,  B,  C.) 

8.  To  determine  the  relationship  of  developing  third 
molars  to  certain  recurrent  malocclusions,  and  also  as  a 
precaution  so  that  steps  mag  he  taken  to  prevent  these 


160 


DENTAL   AND    ORAL    RADIOGRAPHY 


Fig.   109. — An  unerupted  lower  second  bicuspid   in  a  patient  twelve  years   old. 


Fig.   110. — -Unerupted  upper  and  lower  bicuspids  in  a  patient  eleven  years  of  age. 


INDICATIONS    FOR   X-RAY    IN    DENTISTRY 


IGl 


teeth  from  becoming  a  cause  of  malocclusion  dnrmr/  their 
eruption. 

The  pressure  exerted  by  developing  lower  third  molars 
is  often  sufificiently  great  to  cause  a  crowding  of  the  lower 
incisors  and  cuspids.  (See  Figs.  112  and  113.)  This 
can  be  true,  even  though  malocclusion  has  not  existed 
in  this  region  previous  to  the  development  of  the  third 


%jj^ 


B. 


C. 

Fig.    111. — Unerupted    cuspid    teeth    whose    relationship    to    the    roots    of    the    incisors 
must  be  taken  into   consideration  during   tooth   movement. 

molars.  By  making  radiograms  from  time  to  time  of 
patients  at  the  age  of  the  eruption  of  these  teeth,  the 
status  of  the  developing  teeth  can  be  determined  and  the 
necessary  precautions  taken  to  prevent  the  crowding  of 
the  incisors  and  cuspids. 

9.  To  observe  nonvital  teeth  prior  to  tooth  movement, 


162 


DEISTTAL   AND    ORAL   EADIOGRAPHY 


Fig.    112. — An    unerupted    lower   third   molar    which    is    crowding   the   incisors. 


Fig.  113. — An  erupting  lower  third  molar  which  has  been   responsible  for  the  crowding 
of   the   lower   incisors   and    cuspids. 


INDICATIONS    FOR    X-RAY    IN    DENTISTRY  163 

to  determine  their  fitness  for  movement  or  anchorage, 
and  their  state  of  health  during  the  process  of  ortho- 
dontic treatment. 

Where  it  is  necessary  to  either  move  nonvital  teeth,  or 
utilize  them  as  anchorage,  it  is  essential  to  the  patient's 
welfare  and  comfort  to  know  that  such  teeth  and  their 
investing  tissues  are  in  a  healthy  condition.  By  determin- 
ing this  prior  to  instituting  orthodontic  treatment,  much 
trouble,  both  to  the  patient  and  operator,  can  often  be 
avoided.    (See  Fig.  114.) 

10.  In  cases  ivhere  anomalous  teeth  are  present,  to  dif- 
ferentiate hetiveen  anomalous  and  normal  teeth. 

In  a  majority  of  instances,  this  can  be  done  without  the 
aid  of  the  radiogram,  unless  the  teeth  in  question  have 
failed  to  erupt.  Under  such  conditions,  by  utilizing  ac- 
curacy in  the  technic  of  making  the  radiograms,  little  dif- 
ficulty is  encountered  in  determining  the  difference  be- 
tween normal  and  anomalous  teeth.  Examples  are  shoAvn 
in  Figs.  115, 116,  and  117. 

Radiographic  Requirements. — Owing  to  the  fact  that 
patients  undergoing  orthodontic  treatment  are  usually 
children  whose  ages  necessitate  their  being  handled  with 
tact  and  gentleness,  if  confidence  is  to  be  maintained, 
precaution  should  be  taken  to  rid  every  operation  of 
fear  or  discomfort.  Especially  is  this  essential  in  mak- 
ing radiograms,  for  any  considerable  degree  of  move- 
ment on  the  part  of  a  patient  will  either  curtail  the  value 
of  the  finished  radiogram,  or  render  it  useless. 

In  selecting  a  method  of  procedure  for  making  radio- 
grams of  children,  the  child's  comfort  must  be  taken 
into  consideration,  and  with  this  idea  in  mind,  the 
author  has  found  it  an  advantage  to  use  the  extra-oral 
method  quite  universally.  In  fact,  he  has  used  it  in 
nearly  all  cases  except  where  the  region  embracing  the 
upper  anterior  teeth  is  under  scrutiny.     The  wisdom  of 


164 


DEN^TAL   Al^D    ORAL   RADIOGRAPHY 


Fig.    114. — A,   nonvital  tooth   being  used  as  an  anchor   tooth;    B,   nonvital    tooth   which 
was   not  considered   safe   for   anchorage. 


rwy 


Fig.    115. 


Fig.   116. 


Fig.  115. — Supernumerary  upper  second  bicuspid.  Upon  the  extraction  of  the 
supernumerary,    the    normal    tooth    erupted. 

Fig.  116.- — Lower  deciduous  central  incisors  having  the  appearance  of  supernu- 
merary teeth.  The  radiogram  leaves  no  doubt  as  to  their  identity,  and  also  shows 
that  these   teeth   have   no    permanent    successors. 


I  '^' 


Fig.    117. 

Fig.  117. — Radiogram  showing:  either  an  anomalous  central  incisor  or  a  central 
incisor  lying  in  a  horizontal  position  to  the  other  teeth.  The  patient  was  sixteen 
years  of  age. 


loSTDICATIONS    FOR    X-RAY    IN    DENTISTRY 


165 


Fig.    lis. — The   patient   is  seated   and   the   apparatus   arranged   to   make  a   radiogram 
of  the  left  side.     Fig.   99  shows  the  extent  of  radiograms  made  by  using  this  technic. 


Fig.  119. — The  patient  is  seated  and  the  apparatus  is  arranged  to  make  a  radiogram 
of  the  right  side.     Fig.  100  shows  the  extent  of  radiograms  made  by  using  this  technic. 


166  DEXTAL   AXD    OEAL   RADIOGRAPHY 

this  course  will  be  apparent  to  anyone  who  has  experi- 
enced the  discomfort  of  having  intra-oral  films  placed 
lingnally  to  the  lower  teeth,  where  the  tissues  are  very 
sensitive,  or  has  had  them  placed  posteriorly  in  the 
molar  region,  against  the  palate,  where  they  so  fre- 
quently induce  gagging.  These  unpleasant  features  are 
all  eliminated  by  using  the  extra-oral  method,  and  good 
radiograms  of  the  structures  can  be  secured  on  the 
larger  plates.  (See  Figs.  118  and  119.)  This  statement 
should  not  be  construed  as  a  protest  against  the  use  of 
intra-oral  films  in  dental  radiography,  for  it  is  very 
often  necessary  to  use  such  films  with  adult  patients 
where  a  high  degree  of  detail  is  essential,  in  determin- 
ing the  condition  about  nonvital  teeth,  root  canal  fillings, 
etc.  In  orthodontic  practice,  however,  where  we  are 
dealing  with  young  subjects  entirely,  a  sufficient  degree 
of  detail  can  be  obtained  in  the  majority  of  instances  to 
satisfy  the  needs  of  the  operator,  by  using  the  extra-oral 
method. 


CHAPTER  XI 

DANGERS   OF   THE   X-RAY  AND   METHODS    OF 
PROTECTION 

Almost  invariably  when  any  phase  of  x-ray  work  is 
discussed,  some  one  raises  the  query  as  to  the  dangers 
connected  with  it  and  the  injuries  resulting  from  its  use. 
In  fact,  the  impression  is  quite  broadcast  among  the 
laity,  and  to  a  degree  among  the  profession,  that  the 
x-ray  is  a  dangerous  agent  and  as  such  should  only  be 
employed  in  cases  of  dire  emergency. 

This  impression,  erroneous  as  we  know  it  to  be  for 
the  most  part,  gained  credence  as  a  result  of  the  first 
few  years'  use  of  the  x-ra}^,  during  Avhich  period  its 
dangers  were  not  suspected  nor  the  laAvs  governing  its 
use  well  understood.  During  this  period  a  sufficient 
number  of  patients  and  operators  were  injured  so  that„ 
notwithstanding  the  fact  that  mth  our  present  knowU 
edge  of  the  subject  and  with  the  marked  improvement 
in  x-ray  apparatus  these  accidents  are  no  longer  neces- 
sary, the  early  impression  still  prevails  to  a  certain 
extent. 

In  order  that  we  may  not  underestimate  the  dangers 
of  this  valuable  agent  and  consider  lightly  our  responsi- 
bility in  using  it,  we  will  now  consider  the  character  of 
injuries  possible  through  its  misuse. 

We  should  bear  in  mind  the  fact  that  the  x-ray  in 
medicine  serves  a  double  purpose.  It  is  used  as  a  diag- 
nostic agent;  that  is,  in  making  radiograms  and  fluoro- 
scopic examinations,  and  as  a  therapeutic  agent.  In  the 
latter  capacity  patients  are  subjected  to  repeated  ex- 
posures, the  length  of  which  are  very  far  in  excess  of 

167 


168  de:n^tal  aistd  oral  eadiogeaphy 

that  required  in  making  radiograms.  In  fact  the  length 
of  exposure  in  one  average  x-ray  therai3y  treatment  will 
more  than  out-total  the  necessary  exposures  to  radio- 
graph a  half  dozen  patients  for  diagnostic  purposes. 
Therefore,  the  responsibilit}^  of  the  x-ray  therapist,  and 
the  danger  connected  with  his  work  are  far  in  excess  of 
the  man  who  limits  his  activities  with  x-ray  to  radiog- 
raphy alone. 

Of  the  various  ill  effects  attributed  to  the  x-ray,  the 
so-called  ''x-ray  burn"  or  dermatitis  is  the  most  com- 
mon. This  injur}''  occurs  in  various  degrees  of  severity, 
depending  upon  the  amount  of  overexposure  to  which 
the  one  afflicted  has  been  subjected,  and  is  designated  as 
"acute"  and  "chronic." 

Acute  X-ray  Dermatitis 

Acute  x-ray  dermatitis  in  its  simplest  form  manifests 
itself  in  somewhat  the  same  way  as  ordinary  sunburn. 
There  is  a  slight  pinkish  erythema,  dry  in  character, 
accompanied  oftentimes  by  the  sensation  of  tingling  or 
burning.  If  x-ray  exposures  are  continued,  this  condi- 
tion is  augmented  b}''  the  appearance  of  vesicles  and  the 
affected  surface  becomes  moist  or  "weeping,"  and  the 
patient  has  similar  sensations  as  those  produced  by  any 
blistering  burn.  If  exposures  to  the  ray  be  discontinued 
at  this  stage,  the  affected  area  will  slowly  clear  up  with 
no  permanent  ill  effect  except  perhaps  a  slight  pig- 
mentation. 

If  the  exposures  be  continued,  the  next  degree  of  der- 
matitis will  ensue.  The  affected  area  becomes  an  angry 
red  in  appearance,  congestion  is  intense,  and  the  surface 
is  covered  with  a  yellowish  white  necrotic  membrane, 
which  is  epithelial  in  character.  In  fact,  up  to  this  point 
the  connective  tissue  is  not  affected  except  for  more  or 
less  swelling.    This  degree  of  dermatitis  is  exceedingly 


X-EAY   DANGERS METPIODS    OF    PROTECTIOX  100 

slow  in  healing,  months  being  required  for  the  necrotic 
membrane  to  disappear,  and  when  this  has  occurred  it  is 
followed  by  a  horny  epidermis  which  appears  in  spots 
over  the  area  affected,  eventually  covering  it.  This  new 
skin  while  smooth  and  natural  looking  is  usually  char- 
acterized by  the  absence  of  all  hairs  and  follicles. 

The  most  severe  form  of  acute  x-ra}^  dermatitis  is  char- 
acterized by  somewhat  the  same  symptoms  as  those  just 
described,  except  that  they  are  greatly  exaggerated. 
The  degree  of  congestion  is  very  great,  the  necrotic 
membrane  extends  deeper  into  the  tissue,  necessitating 
the  surgical  removal  of  masses  of  dead  tissue  to  prevent 
gangrene.  This  sloughing  or  necrotic  area  shows  a 
strong  tendency  to  spread  and  according  to  some 
authors,  is  apt  to  become  malignant.  With  such  a  der- 
matitis patients  often  suffer  very  intense  pain.  Inju- 
ries of  this  degree  of  intensity  are  exceedingl}^  slow  in 
healing,  a  number  of  years  sometimes  being  necessary 
for  the  process  of  reconstruction.  Even  after  it  occurs, 
the  skin  is  not  natural  in  appearance,  but  hard  and 
horny  and  covered  in  places  with  scar  tissue. 

Chronic  X-ray  Dermatitis 

After  a  person  has  been  exposed  to  the  x-ray  a  great 
many  times  covering  a  period  of  perhaps  months  or 
years,  and  has  had  one  or  more  "burns"  which  Avere 
not  allowed  to  heal  before  new  effects  Avere  added  by 
additional  exposures,  the  dermatitis  which  results  be- 
comes "chronic."  This  chronic  x-ray  dermatitis  is  con- 
fined almost  entirely  to  x-ray  operators  and  others  con- 
stantly associated  with  the  x-ray.  The  hands  because  of 
their  exposed  position  are  most  often  the  seat  of  this 
affection.  The  skin  becomes  thin  and  atrophic  with  red 
patches  of  a  vascular  nature,  and  there  is  usually  an 
entire  absence  of  all  follicles  and  hair.  Codman  describes 


170  dejsttal  and  oeal  radiography 

this  condition  as  follows:  ''In  tlie  less  pronounced 
forms  the  skin  appears  chapped  and  roughened,  and  the 
normal  markings  are  destroyed ;  at  the  knuckles  the  folds 
of  skin  are  swollen  and  stiff,  while  between  there  is  a 
peculiar  dotting  resembling  small  capillary  hemorrhages. 
The  nutrition  of  the  nails  is  affected  so  that  the  longi- 
tudinal striations  become  marked  and  the  substance  be- 
comes brittle.  If  the  process  is  more  severe,  there  is  a 
formation  of  blebs,  exfoliation  of  epidermis,  and  loss  of 
nails.  In  the  worst  form  the  skin  is  entirely  destroyed 
in  places,  the  nails  do  not  reappear  and  the  tendons 
and  joints  are  damaged," 

Another  author  states  that  "while  the  condition  in 
chronic  forms  of  x-ray  irritation  is  as  a  whole  atrophic, 
there  is  usually  a  peculiar  tendency  to  hyperkeratosis, 
which  shows  itself  in  increased  horniness  of  the  epi- 
dermis about  the  knuckles  and  in  the  formation  of  kera- 
totic  patches.  In  some  cases  this  is  very  marked,  so  that 
the  affected  parts,  usually  the  backs  of  the  hands,  have 
scattered  over  them  many  keratoses  with  or  without  in- 
flamed bases.  The  appearance  is  very  similar  to  that 
seen  in  senile  keratosis  where  the  patches  are  inflamed 
and  have  a  tendency  to  epitheliomatous  degeneration. 
The  development  of  epitheliomas  in  these  patches  of  x- 
ray  keratosis  has  within  the  last  feAv  3^ears  been  well 
established."  Carcinoma  may  also  have  its  origin  from 
the  same  source,  in  fact  many  x-ray  operators  who  have 
failed  to  take  the  proper  precautions  have  been  subject 
to  this  dreaded  malady,  the  hands  being  the  parts  most 
often  affected. 

Other  111   Effects 

In  addition  to  the  before  described  injuries,  there  are 
still  other  ill  effects  attributed  to  the  x-ray,  such  as  loss 
of  hair,  sterility,  and  certain  systemic  effects.  The  loss 
of  hair  due  to  x-ray  exposure  is  not  to  be  regarded  seri- 


X-RAY   DANGERS — METHODS    OF    PROTECTIOX  171 

onsly,  unless  it  is  associated  with  a  dermatitis  of  suffi- 
cient severity  to  destroy  the  hair  follicles,  for  unless  this 
complication  is  present,  the  hair  comes  back  within  five 
or  six  weeks. 

The  x-ray  has  a  deleterious  effect  upon  developing  em- 
bryonic cells  and  can  therefore  be  the  cause  of  sterility 
in  the  male  by  destroying  the  spermatozoa,  and  in  the 
female  by  the  destruction  of  the  primordial  o\ailes.  This 
condition  is  brought  about  by  continued  exposures,  and 
x-ray  operators  are  the  ones  usually  affected.  It  is  not 
accompanied  by  impotence,  is  temporary  in  duration, 
and  can  be  avoided  entirely  by  adopting  protective 
measures. 

Eegarding  the  so-called  injurious  systemic  effects  pro- 
duced by  the  x-ray,  too  little  evidence  of  a  convincing 
character  has  ^-et  been  presented  to  really  fasten  the 
blame  upon  the  x-ray  for  conditions  other  than  those 
before  enumerated.  Therefore,  until  its  guilt  is  scien- 
tifically substantiated,  we  must  not  indict  it  for  condi- 
tions which  may  be  but  coincident  with  its  use. 

Methods  of  Protection 

The  evil  effects  of  the  x-ray  can  be  entirely  avoided  by 
utilizing  the  protective  measures  afforded  in  modern  x- 
ray  apparatus.  Inasmuch  as  lead  is  impervious  to  the 
rays,  it  can  be  used  in  different  forms  and  in  various 
pieces  of  apparatus  in  such  a  way  as  to  control  or  con- 
fine the  rays  according  to  the  will  of  the  operator. 

Tube  Shield 

The  most  essential  piece  of  protective  apparatus  is 
the  tube  shield  (Fig.  120).  This  is  constructed  of  leaded 
glass,  there  being  a  sufficient  amount  of  lead  salts  incor- 
porated in  the  glass  to  prevent  ordinary  rays  from  pass- 
ing through  it.     The  sides  extend  up  over  the  highest 


172 


DENTAL    AND    ORAL    RADIOGRAPHY 


part  of  the  tube  and  the  opening  at  the  top  is  often  cov- 
ered Avith  a  rubber  cap,  in  which  lead  is  also  incorporated. 
At  the  bottom  directly  opposite  the  target  of  the  tube  an 
opening  of  the  proper  size  is  left  to  allow  the  desired 
rays  to  pass  out.  The  size  of  this  opening  may  be  con- 
trolled by  interchangeable  diaphragms  of  various  sizes, 
which  are  constructed  of  sheet  lead  about  one-sixteenth 
of  an  inch  in  thickness. 

This  apparatus  is  usually  augmented  by  a  compres- 


^- 


Fig.    120. — An   x-ray   tube   inclosed  within  a  leaded  glass   tube   shield. 

sion  cylinder,  which  is  attached  to  the  base  of  the  tube 
shield,  against  or  in  contact  with  the  lead  diaphragm. 
Such  a  cylinder  is  usually  constructed  of  aluminum  with 
a  lead  lining,  is  made  in  various  lengths  and  diameters 
according  to  the  character  of  the  work  for  which  it  is  to 
be  used,  and  serves  the  purpose  of  confining  the  rays 
coming  through  the  diaphragm  from  the  target  of  the 
tube. 

These  pieces  of  apparatus  are  usually  integral  parts 


X-RAY    DANGERS METHODS    OF    PROTECTIOX 


of  the  modern  tube  stand,  sold  by  all  reliable  manufac- 
turers of  x-ray  apparatus.  It  should  be  apparent  to 
anyone  that  with  such  apparatus,  the  only  rays  which 
leave  the  area  of  the  tube  are  those  which  pass  through 
the  diaphragm  and  cylinder  and  are  used  upon  the  pa- 


^ 


Fig.    121. — Types   of  lead-lined   protection   screens. 

tient.  In  radiographic  work  these  do  not  injure  the 
patient,  as  the  exposures  are  too  short  to  produce  ill 
effects,  even  if  numerous  exposures  are  necessar^^ 

On  the  other  hand  the  radiographer  who  fails  to  use 
these  protective  measures,  or  who  carelessly  places  him- 


174  DEI^TAL   AI^D    ORAL   EADIOGRAPHY 

self  in  the  direct  path  of  the  rays  will  in  time  through 
the  accnninlative  effect  of  the  x-ray  be  very  apt  to  reap 
as  a  resnlt  of  his  foU}^  some  of  the  dread  injuries  before 
described. 

Other  Means  of  Protection 

In  addition  to  the  protective  measures  thus  far  de- 
scribed, there  are  other  means  that  afford  additional  pro- 
tection, and  if  a  person  is  working  constantly  with  the 
x-ray  these  should  be  used.  Among  these  is  the  leaded 
screen  behind  which  the  operator  stands  during  the  time 
exposures  are  made  (Fig.  121).  Such  a  screen  is  usually 
placed  in  front  of  the  controlling  apparatus  and  has  a 
leaded  glass  window,  so  that  the  operator  can  watch  the 


Fig.    122. — Lead-impregnated    glove. 

patient  during  the  exposure.  Lead-impregnated  gloves 
(Fig.  122)  and  aprons  (Fig.  123)  are  also  used  by  some 
as  a  precaution,  but  such  extreme  measures  are  not  nec- 
essary for  the  dentist  doing  his  own  radiography. 

With  a  properly  constructed  leaded  glass  tube  shield, 
lead  diaphragm,  and  lead-lined  cylinder  the  operator  is 
safe,  provided  he  takes  the  precaution  of  avoiding  the 
direct  rays. 

We  all  realize  that  many  very  useful  agents  in  medi- 
cine and  surgery  are  dangerous  when  used  carelessly,  in- 
discriminately, or  may  we  say  ignorantly.  The  old  say- 
ing that  "fools  rush  in  where  angels  fear  to  tread,"  per- 
haps applies  with  greater  significance  in  many  branches 
of  medicine  than  we  would  care  to  admit.    But  the  fact 


X-RAY    DAls^GERS METHODS    OF    PROTECTION  175 

that  through  the  misuse  of  dangerous  agents,  many 
patients  have  met  death,  or  have  been  subjected  to  need- 
less suffering,  is  no  argument  against  their  use  when 
placed  in  competent  hands.     In  such  hands  the  x-ray 


Fig.   123. — X-ray  protection  apron. 


stands  today  as  one  of  the  greatest  adjuncts  to  the  mod 
ern  art  of  healing,  a  blessing  to  humanity,  even  if  in  its 
early  history  it  left  its  martyrs  here  and  there ;  its  bene- 
fits and  triumphs  far  out-balance  any  evils  connected  with 
its  use. 


INDEX 


Alternating  current,  31 

Alveolar   abscesses,   12S,   137 

Ampere,  32 

Anode,  26 

Anomalous  teeth,  158,  164 

Arrangement    of    apparatus,    75,    95 

B 
Broken-off  broaches,  133 

C 
Cathode,   26 
Cathode  rays,  28,  29 
Coil,  37,  39 

primary,  41,  43 

secondary,  41,  43 
Compression  cylinder,   70 
Compression  cylinder,  special,  86 
Compression   diapihragm,   70 
Coolidge  tube,  69 
Crookes,  Sir  William,  27 
Crookes  tubes,  27 
Crown  and  bridgework,   146 
Current  conditions  for  radiography, 

107 
Cj'sts  and  tumors,  134-150 

D 

Dangers  of   the  x-ray,   167 
Darkroom,  76 
portable,  77 
Developer  for  plates  and  films,  120 
Development  of  plates  and  films,  117 
Drying  plates  and  films,  119 

E 

Electric  currents,  31 
alternating,  31 


Electric  currents — Cont  'd. 

amperage,  32 

direct,  31 

high  tension,  31 

voltage,  31 

wattage,    32 
Electrolytic  interrupter,  46 
Electromagnetic  induction,  39 
Electromagnets,  38 
Electromotive    force,    31 
Electrons,  22 
Extra-oral  radiograms,  81-92 


Faraday,  Michael,  25 

Filling     materials,     appearance     of, 

132 
Film  holders,  88 
Films,  x-ray,  117 

film  chest,  116 

preparation   for    exposure,    117 
Fluorescence,  26 
Fractures,  126,  150 


Geissler,  26 


G 


H 


Hertz,  Heinrich,  28 
High  frequency  coils,  53 

diagrams  of,  54 
Hittorf,  26 
Hydrogen  tube,   69 


Illuminating  cabinets,  124 
Impacted  teeth,  126-149 
Induced  currents,  38-39 
Induction  coils,  43 
diagram  of,  44,  47 


177 


178 


INDEX 


Induction  coils — Cont'd. 

essential  parts  of,  43 

illustrations  of,  49,  50,   51 
Interpretation  of  radiograms,  122 
Interrupterless  transformer,   55 

illustrated,  57 
Interrupters,  46 

electrolytic,  46 

mechanical,  46 
Intra-oral   radiograms,   81,   82 

L 
Lead  apron,  174 

Lead  compression  diaphragm,  70,  73 
Lead  gloves,  174 
Lead  screen,  174 
Leaded  glass  tube  shield,  70,  171 
Lead-lined  compression  cylinder,   74 
Lines  of  force,  magnetic,  36 
Low  vacuum  tubes,  110 

M 

Magnet,  electro,  38 

poles  of,  35 
Magnetic   effect   of   electric   current, 

37 
Magnetic  field,  35 
Magnetic  force,  lines  of,  36 
Magnetic  induction,   36 
Magnetism,   34 
Milliamperemeter,  109 
Missing  teeth,  127-164 

N 
Nature  of  the  x-ray,  23-30 
Necrosis,  131 

O 
Ohm,  defined,  32 
Ohm's  law,  33 
Oral  examination,  135 
Oral  surgery,  148 
Orthodontia,  152 

radiographic  requirements  in,  163 


Pathoradiograpliy,  20 
Penetration  of  x-rays,  110 


Pericemental   infection,    137 
Photographic  darkroom,  76 
Plate  chest,  115 
Plates,    x-ray,    115 

care  of,  115 

development  of,   117 

drying,    119 

preparation  of,  115 
Portable  darkroom,  77 
Power  rating  of  coils,  52 
Primary  coil,  43 
Protection  from  x-rays,   171 
Pyorrhea  pockets,  134-144 

E 

Radiogram,  20,  78 

examination  of,  124 

extra-oral,    81-92 

interpretation  of,  122 

intra-oral,  81,  82 

proper    tube    and    current    condi- 
tions for,   110,   111 

rules  for  making,  80 
Radiographic  examination,  complete, 

91 
Rectifier,   chemical,   59  ' 
Rhumkorff  coil,  43 
Roentgen,  William  Conrad,  17-24 
Roentgenogram,  20 
Roentgenograph,  20 
Roentgenolog}',  20 
Root   canal   treatment,   139 
Root  resection,  143 
Rotary   converter,   59 


S 


Secondary  coil,  43 
Self-induction,  42 
Solenoid,   37 
Spark  gap,  52 


Technic    of    radiography,    78,    82-92. 
correct  and  incorrect,  diagram  of, 
83 


INDEX 


179 


Terminology,  20 
Tesla  coils,  53 

Transformers,    interrupterless,    55 
Tube,   connection   to   x-ray  mechinc, 
64 

inverse  in,  113 

regulation  of,  04-107 
Tube  conditions  for  radiograms,  108 
Tube  shield,  74 
Tube  stand,  70 

with  platerest,   94 
Tubes,  low,  medium,  and  high,  110 

IT 

Unerupted  teeth,  126 

Unit  of  electromotive  force,  31 

current   strength,  32 

resistance,  32 

V 

Vacuum  of  tube,  how  to  determine, 
108 
relative    merits    of    low,    medium, 
and  high,  110 


Vacuum  tubes,  62,  108 
Volt,  31 
Voltage,  31 

W 

Watt,  32 
Wattage,  32 

X 

X-ray,  dangers  of,  167 
defined,  23 
dermatitis,   acute,   168 

chronic,  169 
discovery  of,  24 
effect    upon    photographic    plates, 

30 
machines,  43 
nature  of,  30 
penetration  of,  30 
production  of,  23 
protection  from,  171 
tube,  62 

connected  to  the   coil  of  trans- 
former,   64 

essential  parts,  62 

tyi^es  of,  63,  69 

A'acuum  of,  63-108 


Date  Due 


2hi 


32F 


T''"- 


Jj-J. 


AEILiJ. 


^ 


q^ 


^ 


RK270 


COLUMBIA  UNIVERSITY  LIBRARIES  (hsi.stx) 

RK  270  IVI13  1919  C.I 

Dental  and  oral  rarliographv 


2002340925 


